# Sticky  Possible causes for GTOs overheating



## 70455goat (Nov 5, 2007)

All,

I read a few posts about people having overheating problems.

I have a shop in my area that specializes in old pontiacs, specifically GTOs. The owner has been racing GTOs for over 35 years. So I asked him what the most common problems could be and here's his responses:

1. Some aftermarket water pumps have the impeller spaced further away from the plate. Too much space between the impeller and the plate doesn't allow the water to be pumped through the engine properly. The water just cavitates at the water pump and doesn't get sent through the engine.
2. Defective thermostat (very common, just happened to me not long ago) If the thermostat is not opening all the way or not opening at all, the car will definetly overheat. It may also overheat if stuck open, but usually the indication is the heater will not blow out hot air.
3. Retarding the timing to stop engine knock and pinging.
4. Clogged water passages or radiator....common sense.
5. Defective fan clutch. (I've also had this problem)
6. Oversize pully/s which makes the water pump turn slower.
7. Missing radiator filler panel. (if applicable )
8. Missing raidator shroud.
9. Lose/worn belts.
10. Defective/wore out water pump.
11. Driving in Southern California during fire season!

Hope these tips may help someone out.

Dale


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## 05GTO (Oct 6, 2004)

Good information!


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## EEZ GOAT (Jul 9, 2005)

i feel sticky


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## Eric Animal (Oct 28, 2007)

#12 Constant heavy throttle application !


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## 70455goat (Nov 5, 2007)

I forgot.....
#13 Letting wife drive car......No water.


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## seamus2154 (Feb 17, 2008)

When I lived back in NY there was a guy named Nunzi in Bklyn, who was a guru and big racer of pontiacs. Had a very popular garage. He was in the game from day one and I had the same dilema in the eary 80's. He explained everything on your list and added that these cars ran hot right out of the factory. It was such an issue that Gm was going to recalibrate the gauge(to lower) to stop warranty inquiries according to him. It's a poor design that we have to work around and keep everything on the list covered because it is gonna run hot if you don't.


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## Rukee (Feb 8, 2007)

Removing the thermostat could also cause overheating as the coolant will go through the motor so fast it won`t be able to extract heat from the block.


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## Eric Animal (Oct 28, 2007)

seamus2154 said:


> When I lived back in NY there was a guy named Nunzi in Bklyn, who was a guru and big racer of pontiacs. Had a very popular garage. He was in the game from day one and I had the same dilema in the eary 80's. He explained everything on your list and added that these cars ran hot right out of the factory. It was such an issue that Gm was going to recalibrate the gauge(to lower) to stop warranty inquiries according to him. It's a poor design that we have to work around and keep everything on the list covered because it is gonna run hot if you don't.


 Wow ..I remember Nunzi !! I am an old GTO fan from the mid 70,s.:cheers


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## Lil GTO (Jun 27, 2006)

Low Oil

If you are burning or leaking oil at a slow enough rate that there are no obvious signs (black smoke out the exhaust or spots in under the car after parked) and you do not check the oil frequently - oil level gets low, does not cool the engine effectively, the radiator and water pump have to carry more load than designed for - and before ya know it your '67 LeMans blows a hose on the highway half way from Mount Pleasant Michigan to East Lansing. Just hope you are lucky enough to have a guy in a 66 and a half Camaro see everything and stop to help you, drive you to the next exit and find an autoparts store with the necessary parts in stock and take you back to your stricken vehicle.

Or - having someone rebuild the Tri-Power Carbs in your '64 GTO and not have the thick rubber gasket that goes between the manifold and the top of the timing chain cover and use silicone instead - only to have the silicone fail somewhere near White Plains New York while on your way from Cleveland, Ohio to Amherst, Mass. Just hope you are lucky enough to have a friend whose dad owns a rental property about 3 miles away who happens to work at a service station and helps you take the car apart enough to fix the problem and that there is an auto-parts store around the corner that has the correct gasket kit in stock. Just be careful you don't put a pin hole in the radiator in the process.


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## chip_bridges (Nov 24, 2008)

The compression ratio is too high for the gas that is available today.
I read the statement on RRE's website at 

Serious Pontiac Horespower - Rock and Roll Engineering

It made sense to me; my 67 GTO has always run hot because the compression ratio is still at 10.5:1, which is too high. I’m starting to assemble parts for the next engine, it will be 9.5:1 or less.


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## geeteeohguy (Feb 2, 2008)

Chip, I recently put a '65 389 together for a friend using RRE's dished pistons. The engine runs smooth, doesn't run hot, is strong as hell, and doesn't ping on 89 octane fuel! You can bet the next one I do for myself will have those pistons in it!!!


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## Knelson (Jan 16, 2009)

I remember with my old Big block 455 the timing cover had two round pipes that may have been sealed with rubber seals if those are rotted out it would allow the eninge to over heat infact I think those things could be left out during a timing chain install 
and cook the motor right away so if you have exhausted all other options it wont take long to find out the shape of these things.Sorry I couldnot be more informative
but I have forgotten more than I know now damn Its a bitch getting old LOL


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## windharp (Oct 16, 2008)

*overheating challenge to restoration newbie*

Overheating was the main cause of not driving the GTO. After not driving it for over a year, I plan to tow it to my auto mechanic to change out fluids and check brakes, etc (safety check) I am new to the car restoration world and need lots of advice. Appreciate the posts about overheating.


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## HenryG (Mar 31, 2009)

My '65 GTO with '74 400 & '66 Tri-power started overheating a couple of years after I bought it on 2003. I did too many "replace parts" instead of diagnosing.
I replaced the points with a new electronic module before the overheating statrted. Found out the ignition module's wire end metal connector had to be bent up. Instruction photos showed differently. So I lived with overheating for 3+ years due to the metal connector hitting the inside of the distributor cap and stopping the distributor timing advance.
Live & learn.


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## bullet20cc (Apr 4, 2009)

*Running hot*

I installed a flex fan and schroud,3300 cfm and used the 3 washer kit (the large washer) dropped the temp 40 deg. I'm running a built 455.


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## d.reese (Apr 27, 2009)

bullet20cc said:


> I installed a flex fan and schroud,3300 cfm and used the 3 washer kit (the large washer) dropped the temp 40 deg. I'm running a built 455.


Too much timing (advanced too far) can cause over heating also.


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## mrtonegto (Aug 7, 2009)

*Jetting*

Running under size jets will definitely cause overheating.

Also using a water pump with a stamped impeller vs the old cast iron impeller.

If your water pump divider plate is not properly clearanced you will overheat also - the water will not cycle properly.


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## VettenGoat (Jun 19, 2007)

How about the idiot rebuilder (no names mentioned; Ken Stakelum of Stuart/Port Lucy FL) forgets to put the plates in behind the water pump then warranties the motor only so long as it doesn't over heat. Brilliant! That was an expensive and fun one to figure out. Stakelum, if you read this, you owe me for a water pump, thermostat, radiator, and two stainless water pump plates. Thanks for the 800 lb tea-kettle!


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## 646904GTO (Feb 10, 2008)

I found the block to pump water tubes missing in one I fixed last summer. The engine builder was a local guy known for building Pontiacs. I originally had taken it apart to see if the rubber seals on the tubes were leaking and didn't find any tubes to put the seals on.


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## goat670 (Aug 10, 2008)

*some more things to check*



70455goat said:


> All,
> 
> I read a few posts about people having overheating problems.
> 
> ...


make sure you have a spring in the lower radiator hose.
a small hole drilled in tstat to prevent air pockets.
AND I HAVE TRIED ALL OF THESE TOGETHER AND STILL RUNS HOT !!!
JUST PULLED THE ENGINE AGAIN!!!!


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## fheckro (Nov 19, 2009)

I have been running a 400 for the past ten years in my 67 GTO and have tried every electric fan, radiator combo conceivable. operating temp...210 to 220 in summer, 190 210 winter(that's with a 180 thermostat). nothing i did made any difference. All water pump baffles tubes and hose springs were installed i can assure you(I assembled the engine). I tried a Milodon aluminum pump, water wetter, air dam under radiator support, thermostat in or out...no help 

Finally, I switched back to the factory belt driven clutch fan... with factory shroud. operating temp so far = 180(come on summer!). Before... I had two big holes drilled in thermostat to help with circulation and it would take a long time to get to 180 but then keep meandering up.Now, with a factory stock thermostat. it goes right to 180 and sticks there like glue.

Now ... I know someone will probably say "ah ha! it was the holes in the thermostat!" Not so. I started the previous saga with the same stock thermostat. And I can say with certainty that experience has shown me (built my first engine in 1974) that increasing the flow in the cooling system will not make it over heat. I can also say as a mechanical engineer, overheating due to increasing the flow rate is against the laws of physics. 

What I will agree to is that the cooling system for the early GTO's is weak. due to air flow patterns , over size engine for application or whatever, but it is definatly on the verge of overload when in stock trim.


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## RiMZCoat (Mar 9, 2010)

*Had similar problem*

Experienced same frustration over 11 years ago when I had my YS 400 motor rebuilt. Got the short block back and completed the install myself along with the head of R&D at Eastwood, a friend of mine. The car kept overheating at around 230 and always had to pull over after only going about 10 highway miles. Engine rebuilder was useless as far as solving the problem. Ran an infrared temp of both sides of the motor, intake, radiator, exhaust manifolds and the like. Problem was the left side was running 15 degrees hotter than the right side. The solution was multiple things done in succession. All combined, it worked. Car runs on a 90 degree day at 195. First thing we did was run a 5/8 hose from the back of the left head freeze plug to the top of the radiator. Had to weld up two pieces of pipe, one to accomodate the radiator hose and the other for the 5/8 hose. Second, ran a restricted thermostat. Third, installed a 2-row aluminum radiator (equivalent to a 7-core radiator, almost twice the original 4 core radiator). Last, installed an auxillary electic fan in front of the radiator in case I got stuck in traffic. The electric fan will not cool the motor down, but help alleviate from getting hotter when sitting in traffic. The highest the temp has ever gotten is 210. If you are curious to see a picture of the 5/8 hose set up, let me know and I can email you a photo. Purpose of the extra hose is to allow circulation through the left side of the motor just like the right side, which has the heater core and several feet of the same 5/8 heater hose. Hope this helps. A little bit of work, but I haven't had to deal with the problem for the past 11 plus years.


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## Rukee (Feb 8, 2007)

^^That's a good tip! I wonder if you could just run that left head heater hose behind/under the distributor to the right side and "T" it into the heater hose coming from the right head?


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## jetstang (Nov 5, 2008)

So, on my motor, I have the diverter plate installed, the 2 tubes in there, got it all bolted up, then found 2 round seals in my seal kit. Figured they go in between the tubes and plates. Now, I've read this link and figure I'll be tearing the front of the engine back off to install these seals. Anybody out there think it will run without the seals and not overheat???


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## Unclesams (Jun 5, 2009)

Nunzi, what a legendary name I remember from my youth (I think he was already old then) as a big Pontiac man. I have to inquire, are there any members who have added aluminum radiators. I spoke at length with the owner of Rodney Red several months ago and I am considering changing over to one of those radiators for my 69 ragtop which I really enjoy driving around town. Of course I will save my original Harrison radiator for when I restore her since she is original matching #. But let me know if you have used one and if they really improve cooling.


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## xconcepts (Jan 4, 2009)

I just got my 66 back from Texas and she was running around 195 I am told all day long. I get here, the TStat freezes, replaced it with at 180 and now I slowly creep up to 230. I think I just going to go with the aluminum radiator and hope that drops it.


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## GreenMachine (Jul 1, 2010)

For what it's worth I had huge issues with overheating for about 8 years. Overheating issues while waiting in line to pull into a car show, stop and go traffic and the most common problem was I'd park it after a decent summer drive at a coffee shop or store and I'd have to wait over 30 mins for the car to cool down before it would turn over. I'd be at 200 temp on avg.

I was at my final straw and picked up the BeCool Aluminum radiator and electric fan kit. I bought it about 4-5 years ago and cost me $1100. People think I have a blower when I pull up b/c the electric fan is so loud, I forgot the name but it's the one they put on huge HP cars and came with the kit listed for the 67 GTO from BeCool. I have a 180 thermostat put in and handles great in Cali summers. Sometimes after a long drive I'll turn the motor off and leave the ignition on and have the fan suck out the heat for a good 3 mins. You can literally instantly watch the water temp go down when the fan is on. The highest temps I saw was ~210 last week when I was in a huge line to park my car at a local car show. Took about 25 mins to get to my parking spot under hot SoCal sun and idle speed. Parked the car, shut off the motor, left the fan on for about 5 mins while I took my lawn chair out and temps were down to 170.

I know it's expensive and you can probably get a similar set up for cheaper, but for me I'd have to say that was the best money I've ever spent.


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## Claymation19 (Jun 27, 2010)

I'm pretty new to the GTO community - my wife and I finally found a sweet 66 GTO that had a 69 engine in it and we've had it for about 8 months now. And to preface the rest of this, I'm not a mechanical genius and my brother-in-law who is won't be able to come by for a while (he's rebuilt a 69 and 71 from the frame up). Anyway here's my current situation:

It had been running a little hot this summer, but I figured that was to be expected with Tennessee temps in the mid to high 90's. My wife and I were out on an evening cruise and the engine temp hit around 210 on the highway, so I slowed down a little bit to not run the engine as hard, but the temp continued to climb to 220 and I cranked up the heater. I pulled off to the side of the road, but the temp hit 230+ and the engine began to run very roughly (this made me sick to my stomach to hear). I turned off the engine as the temp approached 240 and raised the hood. It was very hot, but wasn't billowing steam or anything, though there was a fair amount coming from the overflow tank by the radiator.

To be safe, I had the car trailered back to my garage. I checked the radiator and there were no problems there, it was a little low on water/coolant and the oil was also low by about a quart. 

The problem now is the car won't start. It turns over briefly, but won't come close to starting. I'm trying to think is there a problem with the water pump? Did the extreme heat the engine reached cause some of the gaskets on the heads to fail? I hope some of you may have some ideas what is wrong now so I can try to get her fixed soon - or hopefully my brother-in-law can save me!

Thanks for reading this rambling problem!

Clay


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## skeeter (Jun 29, 2010)

My 455 run,s hot going down the road at 60 miles an hour, at Idle the car radiator doesnt get over 170 degree's. I let it set in the driveway today at ideal and it would stay about 190 degree's anything above 2000 rpm and the temp. starts rising. The fan is putting out good air. I quess the water pump is the next thing i should look at. Skeeter


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## Rukee (Feb 8, 2007)

skeeter said:


> My 455 run,s hot going down the road at 60 miles an hour, at Idle the car radiator doesnt get over 170 degree's. I let it set in the driveway today at ideal and it would stay about 190 degree's anything above 2000 rpm and the temp. starts rising. The fan is putting out good air. I quess the water pump is the next thing i should look at. Skeeter


A thermostat not opening all the way will do what your describing.


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## khinton (Jun 22, 2008)

*Overheating*

How hot is too hot --I hear GTO's run hotter than many


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## Rukee (Feb 8, 2007)

Well I got the idiot lights, but, I just got back from a long weekend cruze where we were going average 75 mph for 1.5 hrs each way, and when we got back I shot the water jacket on the intake with a raytek laser heat gun and it registered 200* running a 190* thermostat after being shut down for a few minutes. Which is perfect as far as I'm concerned. If it goes to 250-260*, I'd be freakin and shuttin her down.


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## xconcepts (Jan 4, 2009)

I swore mine was overheating, went as far as replacing with an aluminum radiator and electric fan. Found out the temp sensor hasn't been replaced in 30 years.......go figure. Runs at 185-200 in 110 degress in AZ, with the elect fan and aluminum rad.


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## geeteeohguy (Feb 2, 2008)

I would say too hot is about 235 and up. A lot of these cars run for decades and hundereds of thousands of miles at 220 degrees with no ill effects. If it's puking out of the overflow and boiling over, you need to address it. My idiot light equipped '67 seems to run much cooler than my rally-gauge equipped '65 because I never know how hot it is!!


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## Mike Fleury (Sep 13, 2010)

Greetings, new to the forum. Looking forward to exchanging ideas and questions from fellow enthusiast.

My 66 GTO just spent 10 months in the shop of a former Pontiac mechanic. Guy new every inch of the car from memory and corrected a laundry list of issues from a prior amateur restoration. I had the same problem with overheating and we tried all the easy things first: flushed the system and installed a new thermostat, boiled out the radiator (4 core), new high-flow water pump but still running hot. He then discovered that the cooling system would pressurize when first starting up the car which he said indicates when the engine was redone they probably used OEM head gaskets which were made out of steel and prone to corroding. The corrosion is allowing the antifreeze to bypass the back cylinders. He also said running hotter at speeds above 60 was also a tell-tale sign, something he confirmed at the side of the road with his laser heat gun. I'll have to live with it for a year or two until I have the engine overhauled.


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## geeteeohguy (Feb 2, 2008)

I've usually found that when the cooling system pressurizes immediately after start up, that there is a combustion chamber leak into the cooling system. This can be verified by removing the rad cap and checking for hydrocarbons on the upper rad tank. BE SURE not to suck up any water with the exhaust analyzer probe, or you'll wipe out the analyzer!!! Sounds to me like leaking head gasket(s). If you're on a budget and can't get to it for a year or two, try some KW block and head seal. Comes in a copper colored can, available at NAPA. I don't like snake oil, but this stuff is a liquid glass based formula, and I've seen it work miracles. It just may save your engine. I personally would not drive your car until this issue is addressed, either with the block seal or a teardown. The block seal is cheaper and faster, though!!!


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## Indecision (Oct 24, 2010)

According to the rally cluster, mine sits at the ~215 hash mark normally which is ok with me. Today I tried running it on the highway for the first time for more than a minute or two and the gauge went up to just under the 245, but according to the thermometer on the rad cap it was only at 190 (not sure what to think). There was a little coolant under the hood so I kept the revs a bit lower on the way back and it didn't go much higher than the 215 hash again. With 4.11s in it at 55mph it's at ~3300rpm so the highway is going to be a no go untill something changes (most likely the gears.)


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## Backup (Oct 16, 2010)

Claymation19 said:


> The problem now is the car won't start. It turns over briefly, but won't come close to starting. I'm trying to think is there a problem with the water pump? Did the extreme heat the engine reached cause some of the gaskets on the heads to fail?


It may not be as bad as you think. If it acts like it has a dead battery, the starter solenoid may be slightly fried from the excessive heat. My uncle used to have this problem. He ran headers on some of his goats and those ones always seamed to fry the solenoids after a while. He'd replace the solenoid and it fixed it every time. I've had a similar starting problem with mine. From time to time, it will start to crank and just die. It makes about half a revolution before I get nothing or it ticks like a dead battery. My problem is solved by tightening up the ground cable at the block. I've tried about everything I can think of to keep it tight but it seems to find a way of loosening itself every few months. Hope this helps and I wish you luck.


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## geeteeohguy (Feb 2, 2008)

Indescision, the generic NAPA type sending units will cause your temp gage to read high. The right sending unit for your Pontiac can be purchased thru Lectric Limited. It's a vehidle-specific sender, and has a different resistance value than the auto parts special ones. Worked for me. My indicated temp went from 225 to 195-200, where it actually was.


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## Indecision (Oct 24, 2010)

geeteeohguy said:


> Indescision, the generic NAPA type sending units will cause your temp gage to read high. The right sending unit for your Pontiac can be purchased thru Lectric Limited. It's a vehidle-specific sender, and has a different resistance value than the auto parts special ones. Worked for me. My indicated temp went from 225 to 195-200, where it actually was.


Good information. But like said, though the radiator cap read ~195 there was still some coolant under the hood, so I wasn't quite sure what to think there. 

Additionaly, I've been on short jaunts on the highway since and at ~55 the tach indicated ~2900 in opposed to ~3800. So I thought I was losing my mind or somehow left it in 3rd, but it has read ~3800 too. So I'm wondering if I have an elecrical issue somewhere that I need to find. Or maybe I am losing my mind.


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## geeteeohguy (Feb 2, 2008)

Make sure your dash instrument cluster is grounded well. I've had issues with these cars giving weird readings with a poor dash ground. These are old cars with old gauges. They need all the help they can get. I once had a '66 that always ran hot. For ten years, it ran at an indicated 210 plus, no matter what. When I was doing some repair work and generally cherrying it out in order to sell it, I found a faulty ground to the instrument cluster. My "hot" engine now ran at 195 degrees, where it had really been running all the time. The bad ground made the gauge read high. Also, those old tachs are known to read 10 to 20 percent high. Never had one do what yours did, though.


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## Indecision (Oct 24, 2010)

I thought about searching for a ground, I just haven't got the opportunity to do so yet. The other wierd thing is that the tach seems to be consistent (even if it is inaccurate as you say) in the other gears. I plan to do a full set of Autometer Sport Comp IIs eventually, and it's not like i'm racing or anything...yet. Just driving it. I have a long way to go before I get the car where I want it.


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## 67PLUMMIST (Sep 1, 2010)

I just replaced the radiator with an Aluminum radiator which is working well. Does anyone have any suggestions for a 1967 High performance mechanical water pump.


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## bullet20cc (Apr 4, 2009)

*Army*



Indecision said:


> I thought about searching for a ground, I just haven't got the opportunity to do so yet. The other wierd thing is that the tach seems to be consistent (even if it is inaccurate as you say) in the other gears. I plan to do a full set of Autometer Sport Comp IIs eventually, and it's not like i'm racing or anything...yet. Just driving it. I have a long way to go before I get the car where I want it.


If that is you Army stuff, thanks for your service. I spent some time in VietNam. E5.


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## bullet20cc (Apr 4, 2009)

I went to a Meziere electric pump with a 3300 cfm fan and my temp went down 30 degrees. I also run a March Sepertine System with and electric water pump. March says you can't do that??????? I did.
Buy one from Butler Performance and they will tell you how.


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## bullet20cc (Apr 4, 2009)

*Overheating*

Also use a Moroso water outlet restrictor. #63440 they come in 3's use the one with the largest hole.


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## woodro350 (Sep 7, 2011)

*My Temp is fluctuating up and down*



Rukee said:


> A thermostat not opening all the way will do what your describing.


I have a 71 455 that is acting strange, 
First I had one of them chinese radiators that had a 7/8 row and a 5/8 row that was in the car when I got it with fan shroud and clutch fan.
It was overheating and so I decided to buy a new radiator cause I felt the chinese radiator was causing it. I bought a griffin dominator radiator that has 2 1.25" rows in it and I thought for sure that would cool it, Wrong! So I bought a flexlite dual electric fan shroud combo and sealed it up to the radiator and now its running 185 at idle and if I rev it up it climbs in temp.
While going down the road it goes from 180 to 195 then back down and back up and if Im running say 60mph and put it in nutrial then the temp climbs and then I put it in gear and it drops while driving, but if I accelerate then it climbs again, Its really got me puzzled. It has a 180 degree tstat in it.
Also have these fans where they stay on, so there not coming on and shutting off while the temp is acting crazy. 
Can someone help me out?
Thanks.


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## Rukee (Feb 8, 2007)

woodro350 said:


> I have a 71 455 that is acting strange,
> First I had one of them chinese radiators that had a 7/8 row and a 5/8 row that was in the car when I got it with fan shroud and clutch fan.
> It was overheating and so I decided to buy a new radiator cause I felt the chinese radiator was causing it. I bought a griffin dominator radiator that has 2 1.25" rows in it and I thought for sure that would cool it, Wrong! So I bought a flexlite dual electric fan shroud combo and sealed it up to the radiator and now its running 185 at idle and if I rev it up it climbs in temp.
> While going down the road it goes from 180 to 195 then back down and back up and if Im running say 60mph and put it in nutrial then the temp climbs and then I put it in gear and it drops while driving, but if I accelerate then it climbs again, Its really got me puzzled. It has a 180 degree tstat in it.
> ...


Sounds like a flow problem. Either the thermostat is limiting flow or the water pump/plate is. Also check for any hoses collapsing.


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## woodro350 (Sep 7, 2011)

Rukee said:


> Sounds like a flow problem. Either the thermostat is limiting flow or the water pump/plate is. Also check for any hoses collapsing.


Thank you for the information.

The bottom hose is one bendy type hose with spring in it. But I havent changed the thermostat or the water pump.
The temp is very inconsistant and I have dual gauges hooked up to and they read the same.
So I will try the thermostat first. Hopefully thats it.

I have a new problem now.
I hooked these dual fans up with a inline 15amp fuse directly to the ignition post in the fuse block and they come on when I turn the key on and start it and stay running while Im driving but when I turn the key off the engine will stay running for about 2-3 seconds then shuts off, If I disconnect the wire from the fuse block then it shuts right off.
Is there somewhere else that I can hook these in with out it doing that?
Again.. Thank you for your help.


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## likethat (Oct 5, 2007)

Run the fans to relay and the relay to the ignition.


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## woodro350 (Sep 7, 2011)

Ok put the relay inline with the fans and thats now working properly.

But still getting warm after putting new 160degree thermostat and new griffin dominator radiator and flexlite dual fans.
On a cold start up it will climb on up to 160 and stay there at idle for about 15 minutes the start slowly climbing. I was watching the flow of coolant in the radiator and at idle its flowing through the cores but when I accelerate the flow stops coming through the cores. I drove it up the road and it went up to 195 and had to turn the heat on in order for it to level off and come down alittle to about 185-190. 
Is it possible that the impeller on the water pump is slipping on the shaft?


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## woodro350 (Sep 7, 2011)

woodro350 said:


> Ok put the relay inline with the fans and thats now working properly.
> 
> But still getting warm after putting new 160degree thermostat and new griffin dominator radiator and flexlite dual fans.
> On a cold start up it will climb on up to 160 and stay there at idle for about 15 minutes the start slowly climbing. I was watching the flow of coolant in the radiator and at idle its flowing through the cores but when I accelerate the flow stops coming through the cores. I drove it up the road and it went up to 195 and had to turn the heat on in order for it to level off and come down alittle to about 185-190.
> Is it possible that the impeller on the water pump is slipping on the shaft?


I took a heat gun out there to check temps on the block while it was reading 165 and the 2 center ports were reading roughly around 430 on both sides, The front and rear ports on both sides are reading around 295-320. Is this normal?


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## dgoat8u (Jan 10, 2011)

*Running HOT!*

This running hot stuff has me about ready to pull my hair out! I have a 66 gto, original 389, rebuilt .30 over. The car ran cool before i rebuilt it. While seating the rings, it got so hot it started spraying coolant out a pin-hole in one of the freeze plugs. After further inspection i found that the original f-plugs were not replaced during the rebuild. There was no waranty since i put aluminum JE pistons in it, and the shop that did the motor said when i figure out the over heating problem to bring it in for a free carb tune.

Well that was over 15 yrs. ago, and i'm starting to get serious about restoring it now. I just put the old clutch fan back on today, with no better results. I'll probably try the water pump next even though it was replaced with new dividing plates at the time of the rebuild.

Here's what it does: When the motor is under a load, or run at a constant 2500 rpm, you can watch the temp go straight up to 245 on the gauge. (i'm getting some after-market gauges so i can get a correct reading tomorrow) Then let off to idle and it rapidly drops to 180 or so. The heater works good, so i'm sure the thermostat is working. Any ideas?? Thanks!:confused


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## Rukee (Feb 8, 2007)

Sounds like a restricted thermostat, I would replace it with a name brand one. And I've seen brand new ones fail right out of the box too. Also be sure your fan shroud fits nice and tight to the fan with the fan half in and half out of the shroud.


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## 66goatframeoff (Nov 8, 2011)

water pump impeller how old is the pum now seen the fins on the impeller rusted down to nothing..


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## BearGFR (Aug 25, 2008)

Pull the water pump and the plate behind it. Remove the gasket, lay the plate directly on the water pump, and "work" the plate opening (gently) with a hammer/body hammer until it just kisses the pump impeller. Reinstall with a new gasket between them - clearance will now be optimum. Not having this right is probably the #1 cause of Pontiac cooling problems.

Also while you have it apart, make sure that the two short tubes that mate up to the back side of the plate are there and that the rubber seals on the ends of them are in good condition.

What kind of fan do you have? Do you have a shroud? Is it installed such that the fan blades are 1/2 in and 1/2 out of the shroud? Do you have a fan clutch that's in good condition? Is your radiator known to be in good condition and correct capacity?

Those are all things to look at AFTER you make sure the pump plate clearance is right.

Bear


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## peahrens (Jun 7, 2010)

I'm a victim, I'm pretty sure, of item #1...bad rebuilt water pump for my '66. It ran warm before last year's work, then very, very war, (hot) in anything but cool weather. Seehttp://forums.performanceyears.com/forums/showthread.php?t=659536 the attached post about bad impellers/placement on many 8-bolt rebuilt pumps. Supposedly Cardone will address this (it's been 10 months) so I'm waiting, with growing impatience. My before and after says it's the pump, especially since a new radiator was installed...4-core vs 3-core to boot.

http://forums.performanceyears.com/forums/showthread.php?t=659536


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## 42867Goat (Apr 5, 2011)

Back in May/June my 67 would run hot on the highway and just after getting on the off ramp it would climb to 210-220ish. Wanted to do a a route 66 tour in a few weeks so I dropped in an aluminum radiator and my problems disappeared. (I live in the desert) Ive also got the 11 bolt pump despite it being period incorrect. The fan also lacks a clutch, so it runs full speed. I also replaced the heater core sometime before that too. I got the thermostat off the shelf in a local autozone. All in all, temps never got above 180-190 in the 3 day, 700 mile trip, in mid July, in the desert.


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## hotrodharry (Feb 5, 2012)

hey their, new to the forum and was hoping to get some info.I am restoring my 70 judge and i just put the motor back in and when i went to put in the 4 row radiator in the aftermarket rad support i noticed the the flex fan is barely scraping the bottom of the fan shroud .It looks way off center.It is a oem fan shroud and has new core support mounts.I dont get it.something is wrong but i am at a loss.


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## BearGFR (Aug 25, 2008)

hotrodharry said:


> hey their, new to the forum and was hoping to get some info.I am restoring my 70 judge and i just put the motor back in and when i went to put in the 4 row radiator in the aftermarket rad support i noticed the the flex fan is barely scraping the bottom of the fan shroud .It looks way off center.It is a oem fan shroud and has new core support mounts.I dont get it.something is wrong but i am at a loss.


Check your motor mounts, and make sure you mounted the core support to the frame correctly. If you don't get all the rubber biscuits in the correct places it can make the support too "high" or "low".

Bear


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## hotrodharry (Feb 5, 2012)

*70 gto has shroud issues*

I put new motor mounts in and the motor fell right into place with no issues.Are the motor mounts adjustable?Its been a while since i put the motor in but i remember the motor went in really easy. as far as the support i put new rubber mounts in and tryed shimming the support down a 1/4 inch with shims just to see if it would help.It still rubs.It is like a 1 1/2 off center of the shroud opening. If i was to shim the core support down any further it would throw the fenders off.did they make different shrouds for the 70?I thought they were the same 69 to like 72.I dont see how the opening in the shroud could be any lower thoe.Thanks bear for the info.


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## jigaway (Jul 2, 2011)

same thing happened to me with a new Shroud. A high quality one at that. I checked the support and mounts a bunch of times and could find nothing off. I ended up taking a butane torch (lightly) to the bottom of the cowl and gently pulled down/reshaped the area around the bottom where the fan was scraping. I hardly had to do much at all. Worked beautifully.

Good luck

Dan


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## hotrodharry (Feb 5, 2012)

*70 judge shroud issue*

no kidding i guess the fan isn't supposed to sit center in the shroud?Is their a different shoud or are they all the same for 69 to 71?Also i have a 4 core stock radiator and the original flex fan.i was thinking on changing to a 3 or 4 core aluminum radiator and a clutch fan.any thoughts?


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## jigaway (Jul 2, 2011)

Probably should sit in the center. Sure doesn't with my aftermarket shroud. Ames and PY advertise "correct" inject molded shroud for 3x what I paid for mine.. an Original Parts Group shroud. Maybe the high dollar ones fit better? 

Love my clutch fan. It moves some serious air. Somewhere on the boards Bear goes in to good detail about shroud placement, clutch fans and all things in general concerning the like. Search for it. A great read.

Good luck

Dan


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## rickm (Feb 8, 2012)

hey, ive seen some pontiac water pumps ( early 8 bolt ) where the impeller designs are deftnitely questionable. its hard to tell the best design to use. rickm.


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## the65gto (Oct 9, 2008)

rickm said:


> hey, ive seen some pontiac water pumps ( early 8 bolt ) where the impeller designs are deftnitely questionable. its hard to tell the best design to use. rickm.


If you have time to read this thread, you will see some interesting conversations about this very item. Chalk up one more for the cast impeller. - PY Online Forums


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## rickm (Feb 8, 2012)

i read it, thanks. i have the cast impeller on my 65 389. i didnt do any plate tweaking but it seems to be doing its job. i really like gto forum, you guys really help each other out with tech. stuff. to me thats a big part of this hobby.


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## us66 (Feb 16, 2012)

Goats just wanna make us think there is always some reason or another why they run hot.


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## soowee (Feb 29, 2012)

I was advised by the folks at Summit Racing to install an aluminum radiator because (A) I had retro-installed factory air conditioning, and (B) the block had been over-bored, both of which were likely to cause overheating. I had unsuccessfully tried ALL the other remedies. The aluminum radiator seemed to have solved the problem, which manifested as GRADUAL overheating as I drove the car at distance on the Interstate or elsewhere, thus eliminating the possibility of lack of airflow. The myth about slowing down the circulation to allow the water to shed heat in the radiator is illogical BS! The brass 4-core radiator I had was simply not shedding heat FAST ENOUGH!


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## foreevergoat (Oct 24, 2011)

What's up fellows, I just removed my water pump in my 65 Goat so that I can adjust the distance between the plate and the impeller. Ran onto a problem, The plate will not budge I can't seem to get it to come free from the timing chain cover. Anyone else have this problem? Any ideas on how to break it free?


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## the65gto (Oct 9, 2008)

foreevergoat said:


> What's up fellows, I just removed my water pump in my 65 Goat so that I can adjust the distance between the plate and the impeller. Ran onto a problem, The plate will not budge I can't seem to get it to come free from the timing chain cover. Anyone else have this problem? Any ideas on how to break it free?


I wonder if it is just "rusted" to the housing?? Maybe a flat tipped punch and tap around the outside to free it up?? How long has it been since it was last removed??


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## Dave67 (Jan 12, 2011)

The waterpump clearance is definitely an issue, I just reworked my back plate to bring it closer to the impeller (was about .300, Now about .03) and it lowered the temp by about 7 degrees. It still hates stop an go traffic on a hot TX day, but coold down when back on the highway.

My W/P pulley is too large 7.25 should be 5.687 (I think) so I know that is contributing also.


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## khinton (Jun 22, 2008)

Has any one used th Flow Kooler water pump---do they help? The specs make them sound great.


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## Nashville.Clay (Sep 16, 2012)

I had same overheating issues. I swapped to a 4 core. Solid fan and 16psi cap. Havent had trouble since. Also too much antifreeze will cause one to run hot.


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## Chris-Austria (Dec 23, 2010)

The flow kooler pump is good, but what really dropped my temps was a big electric fan with a shroud that covers the whole radiator..


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## BearGFR (Aug 25, 2008)

khinton said:


> Has any one used th Flow Kooler water pump---do they help? The specs make them sound great.


Proper installation (divider plate clearance) is much more important than the type/brand of pump ---- with one exception. I've heard of some pumps that have smaller diameter impellers that don't come anywhere NEAR the divider plate no matter how much you try to adjust it.


Bear


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## bullet20cc (Apr 4, 2009)

*Heat*

I'm running two 455's. 4 core down flow radiator, electric water pump at 35 gallons per minute. 3300 cfm electric fan. 160 degree termostat. My heat problem was not enough fuel at higher speeds. Had to change some air and fuel jets.


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## mrbill (Jan 5, 2013)

*lean condition*



bullet20cc said:


> I'm running two 455's. 4 core down flow radiator, electric water pump at 35 gallons per minute. 3300 cfm electric fan. 160 degree termostat. My heat problem was not enough fuel at higher speeds. Had to change some air and fuel jets.


I was waiting for someone to mention fuel/air mixture. Years ago my 67 Lemans had a 400 and ran hot. I farted with it for a whole summer before someone hinted at a possible lean condition. I found the issue was that my 670 72cc heads had been milled to the max, causing not only too much compression for the octane but changing the mating angle to my intake. Once the engine got to ~180 it also began to leak where the intake mated to the heads.


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## Purple Haze (Feb 27, 2011)

This thread has been a great help! After 3,000 miles I had an overheating problem. I was 400 miles from home and the rad shop figured it was the clutch fan as the last 2 cars he looked at had the same issue!! I changed that.. overheating the same! This time I could not touch the rad (200+ degrees)... but, funny enough, I could grab the top rad hose!! it was hot but not too hot to actually grab!!

Thermostat was my next mission. Changed it out, drilled two 1/8th in holes in the flange for air release. VOILA... runs 180-185

Note... I brought the old one in the house, dumped it in a pot of boiling water and............ it would not open!! Real easy to check these things!! (wish I did it with the new one before I installed it ...DUH !!

Thanx Guys. Ric


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## OHGTOGEORGE (Jun 10, 2013)

I am new to forum. I have a 1970 GTO convertible with air cruise and power everything and have noticed the Temp gauge not moving much at all. I suspect either the temp sensor is not working or the gauge in the dash. does anyone have a good way of testing one or the other or both to see which is malfunctioning??


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## Rukee (Feb 8, 2007)

OHGTOGEORGE said:


> I am new to forum. I have a 1970 GTO convertible with air cruise and power everything and have noticed the Temp gauge not moving much at all. I suspect either the temp sensor is not working or the gauge in the dash. does anyone have a good way of testing one or the other or both to see which is malfunctioning??


With the wire off the sensor and the key 'on' the gauge should be full cold. If you short the wire to ground, the gauge should be full hot. You can test the sensor by hooking up a multimeter to the output of the sensor and the other wire to the base of the sensor. Heating up the sensor in a pan of water the values should go from open circuit to fully shorted as the temp goes up.


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## OHGTOGEORGE (Jun 10, 2013)

Thanks, I will try this.


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## DanT (Jun 29, 2013)

I just got my 67 Tempest running again, sort of. The motor does not have a shroud. Original radiator from the 326 that came with the car. I ordered a shroud for it, flushed the cooling system, changed out all the oil(twice), and I am about to change out the thermostat. I have not had any overheating issues on the highway, just in traffic. I am assuming that the shroud will help a great deal but is the radiator from the original 326 good enough for the 400 at slow speeds? The radiator was rebuilt a few years ago.


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## noahfecks (Jul 28, 2013)

Great ideas on here, have a couple of questions after reading all of this.

-How can I make my fan shroud fit better against the radiator for maximum air draw through the radiator? 

-Anybody have good pictures of how they plumbed in the drivers side head to the cooling system?

-(from a different thread)Anybody have good pictures of how they hooked up the vacuum advance on the distributor? I suspect I have things crossed up here

-Part number or source for correct (and real expensive) fan clutch?


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## bellyache (Jul 13, 2012)

I am new to this probably doing it right but I have 66 gto new motor was over heating before rebuild and still is. has new flowkooler wpump new plates at about 50 thousands new clutch fan tstat cheched carb rich it up 34 deg total timing timed 6 deg before new 4 core rad and shroud has pertronics kit changed heater hose nipple vavle by passed haeter core at idle after 20 min warmup in shop it will slowly build to 200 and 210 on road 220 if in town it has 9 to 1 ps there is no reason for this to be that hot and people put bigger rad in bit is basicly all stock running 92 gas I am lost any ideas


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## Rukee (Feb 8, 2007)

Are you sure it's running that warm?? Do you have a mechanical or electric gauge? Do you have access to a thermal laser gun so you can shoot the water jacket on the intake to see the real temp?


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## Darth (Apr 30, 2011)

I know my girl runs hot because of the gears. With a 3.90 she will burn through a quarter mile but is workin real hard on the highway. Lowering your gear ratio so your motor ain’t runnin 3500 RPM at 55 will help. Also, if the engine hasn’t been rebuilt for modern gas that could be a problem. Leaded gas acted as a lubricant for the engine, allowing you to dial up the compression. M buddy had a Road Runner in high school and that bitch ran hot no matter what because of that. When he started putting lead additive in the fuel and running a higher octane (some AV Gas, and I don’t even know if they still make lead additive anymore) it cooled down considerably.

Also, one of daddy’s friends runs Top Fuel Drag cars. He sad that since my engine was just rebuilt it will run hot initially. He said once it gets “broke in” as he called it, it would cool down.


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## JVM225 (Jun 18, 2007)

My 68 has the idiot lights. Like all idiots, I am clueless as long as it doesn't come on.
But I've been thinking of adding an under dash temp gauge just to be on the safe side.
Can anyone suggest a good reliable gauge/sender combo? Not sure where I would mount the sender though. Anyone have any ideas for that? Common sense would dictate putting it on the front of the manifold where the factory one is, but I would like to keep the idiot light working too if that is at all possible.


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## khinton (Jun 22, 2008)

I did just what you want to do check my posts --they show the entire install


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## khinton (Jun 22, 2008)

1963-68 Pontiac GTO Firebird Fullsize All Models Water Pump Divider Plates 2pc
Member id motorcitymusclecar | Feedback Score Of 31308 | 99.7%
03/11, 01:48PM

$39.00
Buy It Now

+ $6.75

shipping

I bought the "new stainless divider plates" and positioned them on an oem water pump ( with cast iron impellers) there must have been a 1/4 Inch gap between the fins and the divider plate--I FOUND AN OEM DESIGNED ZINK PLATED SET OF DIVIDER PLATES ON EBAY--they needed NO change to get the proper gap--I was blown away!--go to ebay---search--these plates solve all the adjustment problems--look just like the original plates--believe me!! I even had to use a thick gasket rather than a thin one that I had--try them you will be happy you did!--we don't need the stainless plates that don't fit any way--if you keep the proper antifreeze in the radiator they wont rust any way--the oem are steel not stainless--the after market ones don't fit--so why try to reshape them when you can get an exact match of the oem's!!? :cheers


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## rickm (Feb 8, 2012)

all these reasons for running hot are true, but another reason gto owners sometimes do not consider is the split grill on these cars. of course we all love the look but It restricts air flow to some degree. all I had on my '64 was a quality stainless steel flex fan n spacer with no shroud and didn't have a overheating problem. now on my '65 I have I rigid steel fan n spacer with a shroud to keep it cool. I run a 160* t-stat that in reality, keeps the motor around 180* depending on driving conditions.


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## SCG Pontiac (Feb 23, 2014)

I have owned and driven GTO's my entire adult life. I bought my first, a 1967 four speed hardtop in 1970 when I was 16. Raced the car every weekend at Lions, Carlsbad, Irwindale and other tracks around Southern California. Drove it to High School during the week. Never once did it overheat. So what is different today? The Pontiac engineer's knew what they were doing and everything they designed worked just fine. 1970 was a different time , fuel had lead in it. Oil had zink in it and the engines were mostly stock. Very few members of this forum own or drive factory stock Pontiac's each improvement we make changes the intended design sometimes better sometimes worse but always different. Today I went for a 2 hour cruise in a 67 GTO convertible with a 467 stroker and the temp never moved from 210 which is right where it should be. Seems like most of the overheating Pontiac's I read about are the cars with gauges. The cars with no gauges seem to have happier owners. Just my 2 cents. Enjoy your Pontiac's


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## 60mgacoupe (Apr 3, 2014)

I am brand new to this forum, today. I purchased a '67 GTO new. It just turned 100k. It ran hot when it was new. The radiator was not up to the task for the 400 motor. I put up with it until I decided to install a fan and a new radiator. The new radiator helped some, and together with the fan it does not run over 210, even in summer parades. Also, I rebuilt the original Rochester/Carter Carburetor, put it in a box, and installed a new Edlebrock carburetor. Runs great now and doesn't heat up.
I look forward to being a part of this site, thanks!


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## Instg8ter (Sep 28, 2010)

Guess i'll jump in with the counterpoint. I run a factory clutch fan in shroud and like Rick i have a 160 deg thermostat and temp never exceeds 180. My question is should we be running a 180 thermostat to get the temps up around 200 for for better thermal efficiency?


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## Flambeau (Dec 30, 2013)

Hey guys, I want to mention some things I just did to make my '68 not overheat. 

I bough a '68 about 3 months ago, it is 100% stock other than the Edelbrock Performer Carb and it has factory A/C. I live in southwest TX and on the first semi-long trip last month I had the temp light come on (I think they are factory set to come on at 240 or so) and coolant boiled over. After cooling down and limping home, I put in a mechanical temp gauge and realized the car was running around 220-230 constantly and it would want to climb with the A/C on. So, I pulled the water pump and noticed that for some reason I only had the large outer divider plate and that had one 1/2 inch hole rusted through it along with other pitting. The water pump was the original cast impeller type and it looked to be okay. 

So to fix this problem I called AMES and bought a Flow-Cooler pump, high flow 180 thermostat, new hoses, and new stainless divider plates. Then I went all out and got the Be-Cool OE aluminum radiator from Summit Racing. It looks just like the stock original and even comes painted black - expensive but really nice. I had to work the divider plate just a little to get it closer to the impeller and then installed everything yesterday. 

Test drive today went great! It was freekin 95 degrees out and the car ran between 190 on the interstate cruzing @ 70 and eased close to 200 in stop and go traffic all with the A/C on! When I turned off the A/C she stayed right around 188 - 192ish... 

I may not have needed all those expensive parts but I know this summer is going to be 100+ degrees every day and I didn't want to worry about ruining such a beautiful engine. I could have probably done it for half the price if I didn't care about keeping it looking stock. Here are the links to the parts if you're interested. 

P.S. Thank to all the members who helped me diagnose my temp problems!

http://www.summitracing.com/parts/bci-17008/overview/make/pontiac/model/gto/year/1968

Pontiac V8 eight bolt hi flow pump


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## BearGFR (Aug 25, 2008)

Good job - I'll betcha a 10-spot against the hold of a rolling donut that you got the biggest improvement from getting the divider plate "right".

Bear


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## Flambeau (Dec 30, 2013)

BearGFR said:


> Good job - I'll betcha a 10-spot against the hold of a rolling donut that you got the biggest improvement from getting the divider plate "right".
> 
> Bear


Bear, I drove all over town today running errands with the A/C blasting and jamming to AM classic rock out of my one dash speaker and she never got above 190. It was about 85 this morning and much less humid than yesterday. I'm glad I can drive around now and enjoy the car instead of constantly wondering when it was going to boil over and leave me stranded. Thanks again for all your help with this and all my other problems.


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## Vulcangunner (Apr 28, 2014)

The 400 HO in my 68' GTO used to run 200-220 not matter what I did, had to retard timing to stop valve rattle. Milodon pump, 4-core radiator, aluminum intake, new timing cover & plate, removed thermostat guts & left restrictor plate, nothing helped. Got hotter as I slowed down, hottest when idling in park.

Installed an electric VDO temp gauge & yes it was too hot, just like the old gauge was telling me.

I was running a new clutch fan so I installed a flex fan & my temp dropped to 160-175. When I slow down the engine temp drops & if I let it idle parked long enough it will drop to 150.

That direct drive flex fan is moving more than twice as much air as the clutch fan did & that made all the difference. I turned my timing back up & it still runs cool.


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## BearGFR (Aug 25, 2008)

Flambeau said:


> Bear, I drove all over town today running errands with the A/C blasting and jamming to AM classic rock out of my one dash speaker and she never got above 190. It was about 85 this morning and much less humid than yesterday. I'm glad I can drive around now and enjoy the car instead of constantly wondering when it was going to boil over and leave me stranded. Thanks again for all your help with this and all my other problems.


That's great news! Glad to hear that you can enjoy it like it's 'sposed to be now.

Bear


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## oldgoat64 (Jun 26, 2014)

BearGFR said:


> Pull the water pump and the plate behind it. Remove the gasket, lay the plate directly on the water pump, and "work" the plate opening (gently) with a hammer/body hammer until it just kisses the pump impeller. Reinstall with a new gasket between them - clearance will now be optimum. Not having this right is probably the #1 cause of Pontiac cooling problems
> 
> Bear


I have a 64 with a 66 389 and sometime around 5 years ago started having overheating problems only at car shows & parade situations. Once I was moving the car ran cool, between 180 & 200
I have been a professional mechanic for over 30 years & have built at least 10 Pontiac motors.
Bears solution makes so much sense & is so simple. I tried & tested every component in the cooling system, 4 core US Radiator, clutch fans, flex fans electric fans, different T-stats, water wetter, pulling the radiator & have it flow checked & last year out of frustration replaced the W/P and ordered new plates from Ames. The old plate was corroded away & needed replacing. First thing I noticed was how poorly the plates fit was. I had to massage them just to be able to install them. Makes sense the fit between the plate & impeller is off.
I did find a soulution which may be temporary as I am going to pull off the water pump after I find those zinc plates on ebay.
My son found on a rock crawler forum that they use the 95 Ford Taurus electric fan. It is 2 speed with low putting out 2500 CFM & High 3800 CFM.
That fan has a shroud and it covers 90% of the radiator. I hooked it up with relays and it keeps low speed temps around 190.

Glad I found this forum & was able to join. Great information & I'm happy you all are willing to share.


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## AZGrizFan (Apr 1, 2014)

Let me preface this with a disclaimer: I am NOT a mechanic, in any way, shape or form. And I didn't stay at a Holiday Inn Express last night either...so I thought I'd come to the best source of Pontiac info on the internet in search of a solution....

I just took delivery of my "new" '69 GTO Tribute convertible, which supposedly has less than 500 miles on the rebuilt engine, transmission and rear end. I live in San Antonio, and temps here are currently hovering around 100*...On my first little jaunt, I noticed three things: 

a) At highway speeds (65+) the engine seemed to be working REALLY hard, which I attributed to the 3-speed turbo 400 transmission and the gear ratio that has it in 3rd gear by 40 mph, so any additional speed is all RPM's...
b) When initially started, the temp gauge sat right at the mid point of the gauge...after running for a while (just a few minutes) at highway speeds the temp gauge started creeping up to the 3/4 mark, so I slowed down to about 55 and it began cooling back towards the midpoint.
c) The oil pressure, which starts out great, dropped down to the lower 1/4 of the gauge when the engine was running hot, and stayed there even when the temp started coming back down...

After reading this thread, I've gotten LOTS of useful info to share with my mechanic about potential solutions to the overheating problem, but I have two questions...

a) Could the oil pressure problem be related to the running hot?
b) How difficult is it to change the gear ratio to not have the engine working so hard at highway speeds? I don't want to have to drive the car at 50 mph its whole life...seems sacreligious! :mad2::mad2:

Thanks in advance for any additional info. This thread (and this forum) are GREAT sources of info!!


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## Rukee (Feb 8, 2007)

It is normal for the oil pressure to be higher when cold. Also what RPM's are you running at 60mph?


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## BearGFR (Aug 25, 2008)

:agree: Also search on this forum for threads relating to Pontiac engines overheating and how to keep them cool. There have been lots of conversations here on that topic.

and.. Welcome!

Bear


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## grnrch (Aug 3, 2014)

*389 overheat problem*

Hi Richard here new to forum. I'am a 65 GTO owner for 24 years and all this time I have had heating issues none so bad I could not drive it but just never felt it was right. This year things started going south so I tore into water pump found plates and timing chain cover gone on the inside. I thought I had my cooling issue whipped, replaced thermostat, new timing chain and gears, timing chain cover, flo cooler water pump with stainless steel plates 11 bolt, radiator cleaned and boiled out. I was going to a show tonight everything started out fine below 180 with 160 degree thermo got on interstate and in 30 miles temp just stated creeping up to above 220. It was so hot it was moaning spitting steam blew antifreeze out, sat 3 hours I started it right up added water made thermo opened loaded on trailer and brought it home. I have no idea what to try or do next, need help!!!!!


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## the65gto (Oct 9, 2008)

grnrch said:


> Hi Richard here new to forum. I'am a 65 GTO owner for 24 years and all this time I have had heating issues none so bad I could not drive it but just never felt it was right. This year things started going south so I tore into water pump found plates and timing chain cover gone on the inside. I thought I had my cooling issue whipped, replaced thermostat, new timing chain and gears, timing chain cover, flo cooler water pump with stainless steel plates 11 bolt, radiator cleaned and boiled out. I was going to a show tonight everything started out fine below 180 with 160 degree thermo got on interstate and in 30 miles temp just stated creeping up to above 220. It was so hot it was moaning spitting steam blew antifreeze out, sat 3 hours I started it right up added water made thermo opened loaded on trailer and brought it home. I have no idea what to try or do next, need help!!!!!


you can read back in this forum about proper spacing of the plates in relationship to the "vanes" on the water pump. Once you read about it, then the question is did you do the adjustment.


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## grnrch (Aug 3, 2014)

*over heat*

sorry no instructions from ames with this deluxe kit had flow cooler pump and two stainless plates


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## rlslavik (Jun 21, 2014)

LOTS of information here guys.
To be honest my head was spinning after the first 6 pages.

I never saw MY thoughts mentioned so - even though they may be in the last 5 pages - I'll throw them out there.

As a mechanical engineer graduate that majored in thermodynamics, and a 68 GTO owner for 20 years, I've learned a few things (often the hard way) that have helped me with mine. 

The fins/tubes of the radiator must be clean clean clean.
There is an acidic type cleaner commonly used on house A/C that can be used on cars as well. SHINY FINS and tubes go a long long ways.
Used the fin brushes - plastic Harbor Freight $1 - to make sure fins are straight.
The air needs to pass as easily as possible through the fins.

Even SOAP FILM on fins/tubes will decreae the heat transfer.
Clean water rinse.

An A/C "radiator" sitting next to the real radiator WILL slow air passage.
Sad but true.
Remove the A/C the ENGING will run cooler.
Tough call on that.
I live in Memphis.

Use rubber/tin or similar sheets to deflect all possible air from the front of the car into/through the radiator.
In summer, the air is hotter closer to the street (even though heat rises) so try to grab air from up high and deflect it DOWN to the radiator.

Some owners have gone as far as painting their radiator FINS black because it looks cleaner from the front - needless to say this is beyond bad.
Remove/replace it.

Car won't start after shutting it off at the gas station?
Header wrap - insulation woven into a cloth roll is the bomb.
Worth ALL the headaches of removing the headers to wrap/bind them up tight.
Near impossible to do it ON the car but it can be done. 
I had that problem and it kept frying solenoids. 
Now I can LITERALLY grab the headers while RUNNING the engine and they are warm but will not burn. Cools the engine compartment down dramatically and no doubt everything associated with it. Even the temp of the air going into the carb.

They make a similar product for the starter (a shiny insulating blanket) and of course the factory stock or aftermarket solenoid shields help also.

Lastly - after chasing down my everheating 400 one summer and replacing nearly everything but the radiator CAP - I replaced the radiator CAP.
It WORKED!!.
The thermostat inside the cap had gone bad or just dirtied up but the result was the same.
Water will boil and steam at 212 when NOT under pressure and blow out under the hood even though the car is not necessarily overheating.
Upwards of 250+ when pressurized.
If you are constantly smelling coolant and finding moisture under the hood with no visible signs of leaks, replace that cap.

One more - I actually had a friend that thought PURE antifreeze would cool an engine better than 50/50 water mix.
Do NOT make that mistake.
You need 50 percent water to cool an engine properly.
Way better than pure antifreeze.


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## devildawg (Apr 27, 2012)

Greetings everyone. Ive been following the various threads on running hot over the last 14 months with great interest and hope that my experience may help those having similar problems. I have a 65 Tempest sports coupe 326 bored .030 over with a mild melling cam that was running at 200 cruising and climb to 220 stuck in traffic regardless of the air temp.The timing and all other obvious potentials have been checked and the engine was running like that since the rebuild and correct cam break in procedure. Ive been making adjustments over the last year one at a time to see what would ultimately drop the temp to a more comforting level. It now has the 65 Tempest chassis manual recommended 180 thermostat. My research from the chassis manual states that the temp light comes on at 248.I finally found the normal operating temp in the 65 Tempest reliability assurance inspectors guide page 41 under the hot idle speed adjustment and it says adjust at normal operating temp 177 to 182. This manual covers all Tempest,Lemans and GTO motors. One more interesting note is found in the 65 owners guide and says normal operating temp should be 180 or above . If gauge reads 245 take immediate action to find the cause. The following are the items I changed or added with little or no effect 1) high flow 180 thermostat 2) high flow water pump/ flow cooler. 3) divider plate adjusted from 1/4 inch to 1/16. 4) a four core brass copper desert radiator. 5) added a fan shroud. 6) changed from a four blade to a clutched 7 blade.8) a dual electric fan set up pushing with a thermostat set to come on at 200. This kept it from going over 212 stuck in traffic and did help with the peak temp lowering it 8 degrees 9) out of desperation added water wetter. And finally what worked ?? I installed a U.S. radiator aluminum desert cooler radiator that appears stock. Now she runs down the road at 180 and never went over 200 stuck in traffic with outside temp at 95 (HALLELUJAH).I tried to keep it simple but wanted to share my experience and highly suggest after first checking the common culprits as already discussed in previous threads that trying an aluminum radiator first may save a lot of time and money. Ive posted a few slide shows of my restoration on You Tube titled 65 Tempest Restoration for those interested. 
Happy motoring to you all


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## khinton (Jun 22, 2008)

*zink plates on ebay (two GTO,s both w/ heat problems)*

I bought set of these zinc plates on eBay --they are exact copies of the OEM plates and the fit is perfect on the original pump in my 68--no clearance modifications needed ---I Have flex fan (Non A/C car) 180 degree thermostat--runs at 180 on the highway--but can get to 195 in heavy traffic on the same approx 90 degree day.
I also have a 64-389 tri power (65 engine)--it has a flow cooler water pump--the owner at flow cooler said two different things in two different calls about the clearance of the plates -- one time he said if the plates are too close to the shroud covering the fins on the pump that the water can't get in the way it is supposed to--the next call when I mentioned what the guys on the forum said; he said to decrease the clearance to the plates as we are told. So what do i believe now? 
I had a radiator specialty mfg re core 64 rad --they increased the cooling from 84 inches to 142 inches--they said it would make a huge difference--but it didn't? He then told me that because the inlet on the top of the rad is straight above the lower outlet tube (same side of the rad) that that cuts the efficiency drastically; because most of the water runs down the one side--He has offered to add a cooling tube to the bottom so the water outlets on the opposite side (passenger) and says he will do it for (no charge) and he thinks this may be a major problem with hot Pontiac's.--(a lot of guys have tightened the clearance of the divider plates and they still run hot) 
Has anyone tried this?--a good mechanic friend thinks this will help a lot!
I'll post back.:banghead:


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## BearGFR (Aug 25, 2008)

Wellsir, I can tell you from my own personal experience that "plan B" (tightening up the clearance on the divider plate) made a HUGE difference on my car. I'm running an aftermarket aluminum "high flow" pump (don't recall which manufacturer right now).

The thing is, this mod is very easy to do, or undo. Pick a direction and try it. If you don't like the results, then try "the other one". 

Bear


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## Lemans guy (Oct 14, 2014)

Guys, putting a TH350 in my 66 Lemans, need to rout. The new coolant lines, does anyone recall if original trans coolant lines go above or below the sway bar? It looks awful close either way, want to get it right and not bend the new lines. Ripped off the old ones, buts. I can't recall above or below.....it always happens!


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## tiretread (Sep 28, 2015)

Great read. I have this same issue with my 1966 Tempest with the stock rad and 326 engine. Replaced upper rad hose, t-stat, and rad cap. So far so good. Car hasn't spit coolant since I did this. However, I did buy a new water pump, shroud, and clutch fan, for install this winter. 

I read earlier that one of the posters said to make sure that the lower rad hose has a spring in it. I checked and the current one does, but the new one I bought does not. What is this springs purpose and can I just take the old one out and put it in the new one? Thanks for any help.


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## the65gto (Oct 9, 2008)

It keeps the hose from collapsing. If it is not rusted bad, you probably can reuse it.


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## tiretread (Sep 28, 2015)

Much thanks!


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## deanhickey (Apr 6, 2015)

Great information, have a 68 that will benefit from this. thanks again


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## datahoarder (May 14, 2019)

Another thing I have found to be miss-understood is vacuum advance. Additional advance coming from the vacuum advance at idle helps keep your car cool and provides better throttle response.

If someone along the line has removed it put it back 

Also if you have replaced your carb with a holley or other aftermarket carb and the vacuum advance is hooked to the ported vacuum ( as it actually states in some of the installation manuals) change it to a manifold vacuum port. Ported vacuum is an emission control. It removes vacuum advance at idle to raise operating temp and burn the gases more completely.

You want this advance from a performance perspective and to keep your old beast cool


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## rjaerial (Nov 10, 2007)

Here is what fixed my problem.... many years ago. I have a 67 GTO convertible with a 400 engine. I fought overheating problems for years and years. Finally an engineer at LLNL in Livermore, where I live solved my problem. My water pump has two tubes on the sides with "O" rings. Replace them. It also has a metal plate with a hole in the center. The design is to send the water into the impeller through that hole. He said the problem was that the hole was too far away from the impeller and the water would enter but then swirl around and no flow. He had me put the plate on concrete and measure up to the top of the hole. Then put a piece of wood on it and hammer it down about 1/2 inch or so. this makes the front of the hole closer to the impeller and helps the impeller flow the water better. Never overheats now after 20 plus years even in a parade. I have a 180 degree thermostat, the cover that goes around the fan blade and an aluminum radiator which I bought two years ago just because the old one failed. good luck I have had my GTO for 52 years now. Love it..


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## DRDYRAT (Feb 8, 2021)

AZGrizFan said:


> Let me preface this with a disclaimer: I am NOT a mechanic, in any way, shape or form. And I didn't stay at a Holiday Inn Express last night either...so I thought I'd come to the best source of Pontiac info on the internet in search of a solution....
> 
> I just took delivery of my "new" '69 GTO Tribute convertible, which supposedly has less than 500 miles on the rebuilt engine, transmission and rear end. I live in San Antonio, and temps here are currently hovering around 100*...On my first little jaunt, I noticed three things:
> 
> ...


Overheated for years, especially when sitting in SoCal traffic. '67 GTO 400 2 bbl. Never thought to, mine had been missing, but one day put on an aftermarket fan shroud. Problem solved.


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## SLSTEVE (Dec 8, 2020)

d.reese said:


> Too much timing (advanced too far) can cause over heating also.


What is the 3 washer kit you referred to?


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## O52 (Jan 27, 2019)

Its been 12 years since that was posted. Don't think you'll get an answer, not at least from OP


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## Steve "Jackstands" Jack (Jun 29, 2020)

Rukee said:


> Removing the thermostat could also cause overheating as the coolant will go through the motor so fast it won`t be able to extract heat from the block.


Just for a late note here... this "too fast" through the radiator is myth and just the opposite where I went to thermodynamics school!


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## PontiacJim (Dec 29, 2012)

Steve "Jackstands" Jack said:


> Just for a late note here... this "too fast" through the radiator is myth and just the opposite where I went to thermodynamics school!



Yep, and this was recently covered. I'll add the info to this post as well.

Not sure where the speed of the coolant BS originally surfaced on the internet. There are those who don't use a thermostat and simply use a restrictor disk, or even a large washer without issue. I hope this post puts all the "too fast" coolant flow BS to rest.


*From the Stant thermostat website:*

"Thermostat Failures"

A thermostat fails to “open” if the return spring breaks or debris prevents the thermostat valve from fully seating or closing; allowing a steady flow of coolant to the radiator, overcooling the engine - This results in poor warm up and heater performance, increased engine emissions and reduced fuel economy"


*From Hot Rod Magazine:*

"If the coolant temperature never increases up to normal operating temperature, it is likely your thermostat is stuck in the open position. If you know your thermostat is opening but your cooling system still is running a warmer than it should, a solution might be to switch to a high-flow thermostat." 

And Finally, *from the H.A.M.B. website, posted by Ebbsspeed: "Myths."*

For those that cling tenaciously to myths, I am going to take one last crack at forever dispelling the Granddaddy of them all when it comes to cooling systems.

The myth is stated as either:

Coolant can be pumped too fast through the engine for it to absorb enough heat, or
Coolant can be pumped too fast through the radiator for it to cool properly, or
Cooling can be improved by slowing the flow of coolant through the radiator so it cools more completely.

NONE of these is true. The simple truth is that higher coolant flow will ALWAYS result in higher heat transfer and improved cooling system performance.

The reason the myth is so persistent, is that: a) without knowledge of fluid dynamics and laws of thermal conduction it does make a kind of intuitive sense and b) it is based on a tiny kernel of truth, but that kernel of truth does not explain the overall system behaviour and so, interpreted out of context, leads to a completely erroneous conclusion.

So, let's start with the tiny nugget of truth. If you had a sealed rad (no flow) full of hot coolant, and subjected that rad to airflow, yes, the longer you left the coolant in the rad, the more it would cool. However, if you were to plot that cooling over time, you would find that the RATE at which the cooling takes place is an exponential curve that decreases with the temperature difference between the hot coolant and the air. Put another way - when the temperature difference (delta-T) between the hot coolant and the airflow is large, heat transfer (cooling) initially takes place very, very quickly (almost instantaneously). But as that happens, and the coolant cools, the delta-T becomes less, and the RATE at which further cooling happens gets less and less until the point where the coolant and air are almost the same temperature and continued cooling takes a very long time. This is Newton's law of cooling. To illustrate this, recall my "quenching steel in a bucket" analogy.

A good example of this law can be seen when quenching a red-hot piece of steel in a bucket of water. At first, the temperature difference (delta-T) between the red-hot steel and the water is huge - therefore the initial heat transfer occurs at a great rate - the steel initially cools very fast - almost instantaneously. However, after this initial cooling, the delta-T is much smaller, so the remaining cooling occurs much more slowly. If you removed the steel after a second or two - it has cooled a lot - but it will still be warm. To continue cooling the steel to the temp. of the water, you have to leave it in there quite a bit longer - because as it cools - the rate of cooling continually decreases as well. In short - initial cooling is fast, but subsequent cooling occurs more and more slowly until cooling that last little bit takes a long time.

So what does this mean? Basically it means, the longer the coolant stays in the rad, the less efficient the cooling that takes place is - to the point that the rate of cooling is so slow as to be detrimental to overall system cooling. Better to dump the big load of heat right away and go back quickly for another load than hang about waiting for a last little bit of insignificant cooling to happen."

*From Water Pump Manufacturer Flow Kooler:

1.* Doesn't coolant need more time in the radiator to cool?

No. But a lot of people still think so. We have come up with some explanations for the Doubting Thomas.

_Debunking the I Can Have It Both Ways Theory_

The water has to have "time to cool" argument is most common one we hear. In a closed loop system if you keep the fluid in the heat exchanger you are simultaneously keeping it in the block longer. Unfortunately, the block is the part that is generating the heat. Sending hot coolant from your source (engine) through the heat exchanger (radiator) to the sink (air) will transfer heat as long as there is a temperature difference between the source and sink. The engine is still generating heat the whole time so why keep the coolant there any longer than you have to.

_Debunking The Conscientious Electron Theory_

We hear that the coolant has to stay in the system longer to cool but what is heat transfer really but conduction, convection and radiation of electrons. The fluid in your system transfers those electrons based principally on the source-sink differential and the exchange material's transfer rate. An electron moves at varying speeds - Bohr's model has it moving at 2 million meter/second and with a mere 11 million eV boost you can get an electron to 99.9% of the speed of light. Though they move at varying speeds physicists accept that electrons move fast - really really fast. Far faster than the flow rate of the water pump. Your engine coolant's electrons do not know (or care) how fast you send them through the system - they just knows that the source is hotter than the sink and off they go.

_Debunking Grandpa's Flathead Theory_

"But wait a minute, I know Grandpa used to put washers in his flathead to slow the flow and cool his engine." We know people did this too. They still do it but the cooling benefit is not from the slower flow but the increase in dynamic pressure in the block that builds from the restriction. Consider that Grandpa had two flathead water pumps sending twice the volume through the same size radiator core as the Model B 4 cylinder. Too much flow in this no pressure system results in fluid loss. Slowing flow rate helps prevent that. At some point Grandpa maxed out the throughput and began building pressure in his block. Increasing block pressure helps reduce the onset of hot spots on his cylinder walls and formation of steam pockets in his block. This is a real benefit and does help cooling but is only realized when throughput nears capacity or is at capacity. While these restrictions may make sense when your rpm is excessive or your flow rate exceeds your heat exchanger throughput, they do not make sense for most applications. If you doubt this thinking then try this simple Ask Dr. Science experiment; clamp off the lower hose while you watch your temp gauge. Hopefully, you will debunk Grandpa's theory yourself before you experience vapor lock and melt your engine.

Flow restriction is not all bad if it serves to prevent cavitation. Cavitation occurs when a pump turns so fast that you generate lower pressure and air bubbles or vapor forms. These bubbles eventually implode and damage the engine block wall and impeller. Rapidly spinning the impeller can literally rip the air from water but may not actually move the fluid, it's tantamount to turning an eggbeater in a paint bucket. Restricting the fluid flow to raise system pressure in the block may help prevent cavitation at higher RPM but is it necessary for most vehicles? Probably not.

Most vehicles do not need to restrict flow because they do not reach or sustain high RPM. Additionally, thin aluminum radiators already restrict by design e.g. fewer rows of thinner tubes. Restrict it further and you may as well hose clamp the lower radiator hose and we know how that works out. When you face Grandpa on the track you may want your washers, otherwise, keep them in the toolkit.

Simply put, you have a far better chance of keeping your cool with greater flow rate through your heat exchanger and exiting the system than holding it in your heat exchanger while generating heat in your engine block.

*2.* _Low Flow Luddites or..."the guy at the shop said"_

When we are chasing an overheating problem, its common to seek help and who better than the guy sitting at the counter in a parts house or the countless experts begging to be heard on internet forums. They are generally excellent credentialed sources but we sometimes meet a low flow believer who thinks heat exchange is determined by how long the fluid stays in the block and how long it stays in the radiator. We fall back on simple logic. FlowKooler pumps achieve higher flow rates through a better impeller design. The high flow rates are seen far earlier on the rpm curve than OEM and self-professed "performance" pumps which use OEM-like impellers. The flow is more efficient builds block pressure sooner which helps in preventing cavitation. All good stuff which no one would refute. The low flow proponent' s argument of "too fast" begins to falls down when we discuss flow itself. If spun fast enough, even the most poorly designed stamped steel impellers will achieve the same hi flow flow rates. Granted they may cavitate, they may pump less efficiently and it will always occur at higher rpms. The point here is whether a discount design pump was spun at hi rpms or our well designed pump was spun under normal driving conditions; flow is flow. Can it be logically argued that a hi flow pump flowed coolant too fast if an OEM pump achieves the same flow rates. No, it cannot.


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## BearGFR (Aug 25, 2008)

But! It's on the Internet! It has to be true, right?


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## Steve "Jackstands" Jack (Jun 29, 2020)

PontiacJim said:


> Yep, and this was recently covered. I'll add the info to this post as well.
> 
> Not sure where the speed of the coolant BS originally surfaced on the internet. There are those who don't use a thermostat and simply use a restrictor disk, or even a large washer without issue. I hope this post puts all the "too fast" coolant flow BS to rest.
> 
> ...


Good points all Jim..... I'd like to explain the "restrictor" or "washer" trick. I think the "slowing the coolant" myth started over in the racing sites. Many cooling systems exhibit laminar flow throughout the system. One common point that is susceptible for laminar flow is out the top of the intake into the outlet hose. Some thermostats when wide open may provide enough interference to stop this flow phenom. And certainly running without a thermostat exaggerates the problem. What the washer insertion does is introduces turbulence to output stream of coolant thoroughly mixing the coolant. This even continues to vigorously mix in the radiator. (It's like jumping in the proverbial lake in the summer and having hot water on top... and cooler water at depth even tho the lake/river is moving. That's the perfect analogy of laminar flow!). If it helps any, I used to be a technical writer for several print media a number of years back. The ONLY copy of my cooling tips as edited by the site provider is here: HOTRODSRJ’s TOP TEN COOLING SUGGESTIONS FOR YOUR ROD(S) enjoy.... I hope I'm not over-stepping my welcome here!


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## PontiacJim (Dec 29, 2012)

Steve "Jackstands" Jack said:


> Good points all Jim..... I'd like to explain the "restrictor" or "washer" trick. I think the "slowing the coolant" myth started over in the racing sites. Many cooling systems exhibit laminar flow throughout the system. One common point that is susceptible for laminar flow is out the top of the intake into the outlet hose. Some thermostats when wide open may provide enough interference to stop this flow phenom. And certainly running without a thermostat exaggerates the problem. What the washer insertion does is introduces turbulence to output stream of coolant thoroughly mixing the coolant. This even continues to vigorously mix in the radiator. (It's like jumping in the proverbial lake in the summer and having hot water on top... and cooler water at depth even tho the lake/river is moving. That's the perfect analogy of laminar flow!). If it helps any, I used to be a technical writer for several print media a number of years back. The ONLY copy of my cooling tips as edited by the site provider is here: HOTRODSRJ’s TOP TEN COOLING SUGGESTIONS FOR YOUR ROD(S) enjoy.... I hope I'm not over-stepping my welcome here!


All good points which have been covered here. Early vehicles did not use pressurized systems, but they have big radiators to keep things cool - they also had 6.0 compression and don't turn a lot of RPM's which doesn't generate a whole bunch of heat. My '48 International truck is made like this.

You missed: when in stop and go traffic and the engine temps start to climb (especially with an automatic), put the trans in neutral and raise the engine RPM's to increase the fan speed and air flow through the radiator -this is right in the Plymouth owners manual and what I do with my '73 Fury as Mopars have issues running hot/trapping heat due to the way the engine compartment is designed. It does pull down engine temps.

How about installing a separate trans cooler if running an automatic? Hot trans fluid can add unwanted heat back into the radiator. This is not really needed in most stock cars, but use a torque converter that has a lot of slip and it generates a lot of heat - and heat breaks down trans fluid. I typically add a cooler on my HP cars and a car/truck that may be used for towing. If you have a really heavy fat chick in the passenger seat, this will also make an automatic trans work harder hauling her butt around, so you may need a trans cooler in this instance as well.


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## Steve "Jackstands" Jack (Jun 29, 2020)

PontiacJim said:


> All good points which have been covered here. Early vehicles did not use pressurized systems, but they have big radiators to keep things cool - they also had 6.0 compression and don't turn a lot of RPM's which doesn't generate a whole bunch of heat. My '48 International truck is made like this.
> 
> You missed: when in stop and go traffic and the engine temps start to climb (especially with an automatic), put the trans in neutral and raise the engine RPM's to increase the fan speed and air flow through the radiator -this is right in the Plymouth owners manual and what I do with my '73 Fury as Mopars have issues running hot/trapping heat due to the way the engine compartment is designed. It does pull down engine temps.
> 
> How about installing a separate trans cooler if running an automatic? Hot trans fluid can add unwanted heat back into the radiator. This is not really needed in most stock cars, but use a torque converter that has a lot of slip and it generates a lot of heat - and heat breaks down trans fluid. I typically add a cooler on my HP cars and a car/truck that may be used for towing. If you have a really heavy fat chick in the passenger seat, this will also make an automatic trans work harder hauling her butt around, so you may need a trans cooler in this instance as well.


I personally have never had any luck just revving the engine to get more fan speed to substantially work. Then again... all my builds (hotrods, classics, muscle cars) have a designed or redesigned cooling system from the get-go that should more than cover the build. I'm in Georgia and street/tarmac temps out front of the car in traffic can reach in excess of 140 degrees in stop/go traffic in the summer! Just keeping off someone's rear end by 20 feet can affect the incoming cooling airstream ambient temperatures significantly. Of course add air conditioning and it complicates the whole thought/design process. I am ready to switch to an original footprint, all aluminum radiator for my 69 GTO (it actually has the large radiator in it now). I only use large-tube aluminum radiators in all my cars. By upgrading to these newer-fangled aluminum radiators, you can easily add 25 to 35% in increase cooling capacity combining with a high-flow water pump (really looking for "high-flow" at lower idle speeds moreover). Many years ago I worked/consulted with Griffin Radiators and TuffStuff Performance to perfect their product lines specifically in the cooling department. It was a real eye opener to combine an aluminum 1.25" dual row radiator with a high-flow TuffStuff water pump. The measured flow(s) was up to 55% better than stock at idle and off-idle conditions! 

I never use trick transmissions and a lot of my cars are manual anyway (maybe a shift kit here and there)... so when I have an automatic, I use the built-in tranny cooler in the radiator. I've never had any tranny issues... so I am sure many here have a lot to offer in this department... fat and buddies chicks aside! 😆

Ever go to "Cruise the Coast"?? That event will definitely tax your cooling system and test as to what you limits are. Sitting in south Mississippi traffic at an event that hosts thousands of cars on the streets during early Oct can be a "cooling" surprise. Let's face it, many of these muscle/pony cars were never designed for enduring the traffic and heat of today's environments. Same thing sitting up at Pigeon Forge events early September... long traffic waits in what can be mid 90s heat! I went to a race up at Michigan (I believe the USAC Twin 200S) in Aug 1970, and it was sweltering hot! There is NO easy path to that facility so got caught in miles of traffic going in my 1970 Grand Prix SJ. Of course we had the air a'blowin and that car started to pop-off the radiator cap every few miles. This car was still on warranty and so by that next week I had it returned to the Pontiac Dealership to investigate. The service manager remarked that they got both GTOs and Grandprix back all the time with over-heating issues. So, the design therein is what was a problem.


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## Lemans guy (Oct 14, 2014)

Steve great insight here. Points all well taken. I would just add that a good flush is important as well. We all say well, that motor was rebuilt a few years ago with all new cooling system.

I looked inside and it looked good. But rust puts a thin film inside radiators and engines and effects heat transfrer.

I just posted about a new product for a coolant system flush, Bear made it a sticky. But if the system has not been flushed in a few years, even with low mileage a good flush can aid in your heat transfer.


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## tallrandyb (Jun 12, 2021)

rickm said:


> all these reasons for running hot are true, but another reason gto owners sometimes do not consider is the split grill on these cars. of course we all love the look but It restricts air flow to some degree. all I had on my '64 was a quality stainless steel flex fan n spacer with no shroud and didn't have a overheating problem. now on my '65 I have I rigid steel fan n spacer with a shroud to keep it cool. I run a 160* t-stat that in reality, keeps the motor around 180* depending on driving conditions.


I know this is old, but do you have a part number for the 160 tstat? I live in Florida so I'm considering dropping my 180 to 160 so it has a chance to run cooler. I have an aluminum radiator and that helped immensely. Thx.


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