# Rebuilt 455 in 66 GTO overheating



## thor7726 (Sep 2, 2012)

Hey Guys,

I put my freshly rebuilt 1970 455 with quadrajet 7040268 in my 66 GTO and at idle or traffic driving it slowly heats up until it overheats in a few minutes. Driving down the road it runs great at 180-200. Here is what I got and have checked:

A.) no 64' 87cc heads 
B.) 9.7 compression Ratio
C.) 93 octane
D.) High cylinder deck to piston quench at 0.018"
E.) Bored 0.03" over
F.) Ram air 4 cam
G.) 4 speed
H.) Factory log exhaust

1.) Water pump replaced and with baffle close to impeller.
2.) 66 4 core radiator, tested good for flow and pressure.
3.) 66 declutching fan with half in half out of shroud.
4.) New belts that are not slipping.
5.) Tried both 180F and 160F thermostat new
6.) New hoses with inner springs to keep from collapsing.
7.) 66 'pan cake' air filter. (Probably restrictive)
8.) 2" duals (Probably Restrictive)

After all of this could it be the carb is out of tune and causing it to run hot? Or the distributor? It is my first quadrajet and maybe its running lean??? Or does a 1970 455 require a bigger radiator and fan than a 66???

Thanks in advacne for any help!
Pete


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## Rukee (Feb 8, 2007)

Is the clutch fan new? Sounds like it might be bad.


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## thor7726 (Sep 2, 2012)

The clutch fan is a few years old. How do I know if it is kicking on? We tried a plastic ice cream scoop fan without a shroud and had the same overheating issue.


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## PontiacJim (Dec 29, 2012)

Could be a number of things. So start simple.

Assume you have a water pump with the cast impeller and not the stamped steel impeller. These don't seem to be as good as the factory cast style. Impeller could even be slipping on the shaft, but I have never seen this.

Belts are not slipping? Some replacement belts are actually thinner than the factory belts and they sit too deep in the pulley and will slip at speed. Looks and sounds good to the ear, but it is not gripping the pulley as it should and things are indeed slipping - learned that one myself.

Your timing may be retarded. Retarded timing will cause an engine to overheat. Yep, I know what the book says, but you may want to play around with it. If you retarded it because the engine was pinging, getting detonation, or it was retarded to make engine starting easier, then that could be the cause. 

There was a recent forum on setting up a distributor with the correct timing curve AND vacuum advance. One of the most important things in setting up a Pontiac to run and keep its cool. The RAIV cam may not produce enough vacuum for the dist. vacuum can presently on the distributor. They come in a variety of vacuum settings or the aftermarket adjustable style. Do a search and you should find it.

Do you have the correct radiator cap? Too low a pressure will allow your radiator to boil over sooner than it should. 50/50 anti-freeze mix? I have used the product called "Wetter Water" and it seemed to lower the water temp in my '68 Lemans with 400 that I was having cooling issues with.

If you throw your inside heater fan on high and your controls all the way to hot (and get ready to sweat), does the temperature drop? This is like adding more radiator. It will cool initially, but will it continue to cool rather than creep back up? 

Have you tried another temperature gauge & matching sending unit? We have had cases where the replacement temp sender that goes into the block is a generic replacement and not an exact replacement from a reputable Pontiac parts supplier. The calibration is off. Many will recommend a infra-red heat gun to check - these can be bought inexpensively at most auto parts stores. You can then shoot the engine, radiator, hoses, etc. to see if you have any problem areas. Your radiator may have been tested to flow "good" (compared to what???), but it does not mean it is working to optimum needs if something is clogged up.

The Q-jet _could be _running lean, but I would not think lean enough to overheat the engine. Pull the plugs and see what color they are and make sure you don't see small flecks on the nose insulator - bad news if you do.

Is the RA IV cam the exact same specs as factory? The Wallace Dynamic Compression Calculator says you should have a 6.35 to 1 compression which is good and should not give you any problems.

The 2" exhaust pipe, in my opinion, is not helping any. I would go with a 2.5" minimum with a crossover and good flowing mufflers. The exhaust may be acting as a restriction in this case and that will heat up an engine.

Is your clutch fan new? These do in fact wear out even though it is spinning. It is designed to really cool at lower RPM's, ie cruising and stop and go. I would replace this if it is not new. The one that seems to be the best recommend is the H-D Hayden brand part #2747 (click here Hayden Fan Clutches 2747 - Free Shipping on Orders Over $99 at Summit Racing ). You may need a fan hub spacer which is easy enough to get should the fan not be far enough into the radiator shroud. The fan blade recommended by many is the factory GM 7 blade 19" curved tip - which you may already have. They were used on Pontiacs, like the '73 455 Grand Prix. You may have to change/modify the shroud as you want the shroud opening to be 1" or so larger and the fan about 1/2" to 3/4" out of the fan shroud. I went with a flex fan on my Pontiac 400 and it did a world of good over the factory solid piece. Don't care for the clutch fan set-up, but many swear by them and they do seem to work.

I rebuilt a 360 CI in my brothers '73 Plymouth and he had a new 3-core brass radiator. Never could get the temps down at idle/stop & go. Put in a new aluminum radiator and problem was solved.

So bunch of things to check and rule out. :thumbsup:


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## thor7726 (Sep 2, 2012)

Thanks for the detailed response Jim! Below are some answers to your post:
1.) My new water pump from NAPA has a cast impeller. When at idle and thermostat is open, radiator cap removed there is flow of coolant. When rev’d up there is even more flow. I’m thinking the pump is adequate. But I’m not ruling anything out yet.
2.) Belts seem good, I tightened the alternator and power steering good and they seem to be gripping. 
3.) We have messed with the timing between 8-11 degrees advanced. I did check that the harmonic balancer zero timing mark was correct to TDC. The one I took off during rebuild had slipped several degrees!
4.) Will check vacuum soon and do the curve.
5.) It is an original 66 cap, we tried a cap off of my dad’s 65 GTO and didn’t make a difference. I’m going to try the wetter water. Doesn’t seem like it will hurt anything.
6.) When I first put the motor in and got stuck in traffic I turned on the heater and it started lower the temp. I didn’t stay long enough to see if it fixed the issue though.
7.) I need a IR temp gun bad. I don’t think the gauge is off, they are old Stewart Warner gauges and you can watch the temp of the thermostat opening and its within several degrees. The engine compartment is just hot, way hotter than my dad’s 65 that runs at 180.
8.) Below is a picture of the plugs, they look really good. What do the small flecks mean on the insulator mean?
9.) Cam grind is the same as the originals.
10.) I really wish I could get a 2.5” pipes exhaust with cross over and ram air manifolds. Maybe next year if budget allows.
11.) Clutch fan is a few years old. I took it off when it was hot and it was defiantly harder to spin so it appears that it is working. (Also tried another fan, see below)

A few nights ago my dad and I decided to pull the radiator and declutching fan from his 1965 GTO 389 Tri-Power. The car runs a rock steady 180 degrees and has been on the power tour. It’s the same size radiator and fan that came out of the 66. The 65 has a different inlet on radiator but a flexible radiator hose and a bunch of work later we had it in and took the 66 455 with the 65’s radiator and fan for a spin. No luck, same exact problem. Runs cool going 55 mph down the road, as soon as it’s at idle or traffic it keeps creeping up until I start moving again or turn it off. We put the radiator and fan back in the 65 and took it for a spin and it is still 180F, cool as ever. 

Therefore, we decided to open the wallet and buy a brand new 4-core Desert Cooler Aluminum Radiator. I think the 66 and 65 radiators just don’t have enough cooling capacity for the 455. The parts are coming in Friday and I should have them in the car by the weekend. I’ll post the results this weekend. Thanks again.


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## PontiacJim (Dec 29, 2012)

Keep in mind that a freshly rebuilt engine sometimes runs hotter until it gets some miles on it.

Flecks on the insulator nose would be small bits of aluminum, ie from detonation/damage to pistons. Your plugs look OK.

Sounds like you have done much work to eliminate many things that it could be, and I'm not sure I have any more words of wisdom as you have done a lot of what I would do. 

Here is something I like to do with the thermostat. I would use a 160. I usually drill three small 1/8" holes, equally spaced around the brass ring - not so far to the edge that it doesn't seal. This will allow any trapped air in the system to escape. You could have a "bubble" some where and the coolant isn't getting to where it needs to be -but this is just an idea to think on. Many of us here can tell you that even a new T-stat can be bad right from the start. Perhaps try another brand. You can also test the T-stat opening temp in a pot of boiling water and a thermometer on the stove top.

The fact that you did try the heater core/blower and the temp lowered, might indicate that you need more radiator, but that is not a guarantee. The aluminum radiator will prove/disprove this. Again, same issue on my brother's car, as Plymouth's do run hot under the hood, and the aluminum radiator was the answer.

The 400 I rebuilt in my Lemans ran just like you described. New 4-core radiator. I did not clearance the water pump impeller/divider as I didn't know about this. I tried different things and used the heater to keep it running cooler when it began to creep near 215 degrees, but sometimes in heavy stop and go traffic on a 95 degree day, it didn't work so well, and water would go out the overflow as it began to boil over - I'd have to pull off the road, but this only happened a time or 2. I used the Wetter Water which seemed to help and then I added a good aftermarket flex fan. This helped a bunch as long as I was moving. Then one day my temp dropped way down to just over 160 and the darn engine never heated up again. Never did figure the cause - completely stumped.

So hopefully the aluminum radiator will do the trick.


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## thor7726 (Sep 2, 2012)

Well, unfortunately the 4-Core Aluminum Desert Cooler didn't fix the overheating at idle issue . It helped, it runs cooler going down the road but within 7 minutes of idling its back up to 220F and not stopping. We ordered a 6.5" water pump pulley and a 17" 7 blade. The Flex-A-Lite fan will also remove the unknown of the declutching fan working or not. I'm working on determining if I need smaller belts or not or if there is enough adjustment to make it work. Does anyone have experience using the 6.5" pulley from Ames? My dad also messed with the timing and nothing changed.


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## PontiacJim (Dec 29, 2012)

thor7726 said:


> Well, unfortunately the 4-Core Aluminum Desert Cooler didn't fix the overheating at idle issue . It helped, it runs cooler going down the road but within 7 minutes of idling its back up to 220F and not stopping. We ordered a 6.5" water pump pulley and a 17" 7 blade. The Flex-A-Lite fan will also remove the unknown of the declutching fan working or not. I'm working on determining if I need smaller belts or not or if there is enough adjustment to make it work. Does anyone have experience using the 6.5" pulley from Ames? My dad also messed with the timing and nothing changed.



Wow, the radiator did not help. That almost indicates that the water is not circulating or that fan is not pulling enough air. Just for kicks, pull the thermostat out completely and see if it changes anything. Won't take to long to try that as a test.

What is your timing set at? What is your maximum advance at 3,000 RPM's? Still could be in the timing & distributor. If the timing is retarded to much, the temp will climb just as you described as I learned this on my engine when I first fired it up and the water temp soared. I called the cam manufacturer to make sure it wasn't a by-product of the cam selection I had chosen and he said "no", that the timing might be too retarded and to advance it. Did that and the engine did not soar in temp - but then I told you I still had cooling issues that I never figured out what it was and it just fixed itself.


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## Pinion head (Jan 3, 2015)

What timing cover/ water pump design are you running? I see non AC two groove pulleys in your picture. If you are running the early 8 bolt timing cover, the design and clearance of the cast impeller is CRITICAL. Personally, I would swap over to the correct AC sized water pump and crank pulley,and pull the water pump and post multiple pictures of the impeller. Every year I typically do half a dozen original water pump rebuild sessions, 6-10 original pums at a time. have learned a bunch examining original cores and what gets sold as a parts store rebuild. '63-64 waste pumps, for instance, use an impeller with very small vanes. this worked with both the inlet and outlet on the pass side of the '64 radiators. '65-68 8 bolt pumps took another style cast impeller. unfortunately, many rebuilders often dig through a bin and find donor impellers that are incorrect and cause incorrect flow.

If engine has been upgraded to 11 bolt timing cover, '68+ damper, '67-70 PS pump and '70 pulleys, I would again pull the pump and post pics of the impeller. There are a lot of short vane 301 impellers out there that work fine on short fill hard block treated stock 400-455 blocks, but the vanes of the impeller do not move enough water in a normal full coolant path 455, ESP when installed in '64-67 Pontiac with the up/down flow radiator. Again changing over to the correct AC application wp, crank, and PS pulley would help with cooling.

Jim mentioned lean carb mixture above. Both short timing and rich, OR Long timing and lean are not good for proper cooling.


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## thor7726 (Sep 2, 2012)

I rebuilt the motor so that it is factory correct for a 1970 GTO or Grand Prix except for the air cleaner and distributor. The pulleys/power steering is 1970 parts (Someday big plan is to put the engine in a 1970 GTO).The water pump is a new 11 bolt from NAPA with cast impeller. I'll pull it off if the smaller pulley and flex fan doesn't work along with trying it without a thermostat. I was gone most of the weekend and my dad had time so he advanced the timing probably a total of 20 degrees and nothing changed. It might just be a tight motor that needs breaking in? Thanks everyone for all your input! I learning a lot!


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## thor7726 (Sep 2, 2012)

Alright, We had put the 6.5" pulley and 17" 7 blade flex-a-lite fan with aluminum desert cooler and it worked the best so far. But at idle, again it would slowly creep up and eventually over heat. In 20 minutes it would over temp... I think I have the worlds hottest most expensive boat anchor. We also discovered that the radiator has a dent by the cap causing a small leak (will have new one by Wednesday). We also tried removing the thermostat, no change. When stopped and you rev it up is will cool down slightly and hold steady. I'm loosing what little of my mind I have left. We have moved the timing all over except severe retarded.

Here are a few more test we came up with:
1.) Check exhaust: Space exhaust pipes 1/2" from exhaust manifolds to allow freer air flow and see if the 2" pipes are too restrictive.
2.) Electric fan: Looking into added one.
3.) Water pump is coming off again to check it over one last time and make sure everything is good and mating correctly. I want to make sure the baffle is mating to the the gaskets that go into the block.

More questions:
1.) Does the ram air 4 cam make a 455 run hotter? 
2.) Could my valve adjustment be off and causing overheating?
3.) Are head gaskets from Butler ambidextrous? Did I put them on wrong?
4.) Did I put the intake gaskets on wrong? IS there a trick I didn't know about?


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## oldskool (Apr 26, 2015)

"...3.) Are head gaskets from Butler ambidextrous? Did I put them on wrong?..."

Yes, they can go on either side of the engine. But, the metal side goes down to the block--the other side goes up to the head. And, as per instructions, the metal side gets 2 light coats of Copper Coat. :smile3:

Butler Performance - Pontiac Head Gaskets

Also, the BP gaskets are .045 thick. Add that to your stated deck height of .018, gives you .063 quench distance. .040 is recommended. That might contribute some to the extra heat.

"...1.) Does the ram air 4 cam make a 455 run hotter?..."

Never heard that.

"...does a 1970 455 require a bigger radiator and fan than a 66???..."

Wasn't the radiator core size on a '70 GTO, bigger than on a '66 ? If so, it would hold more coolant, and have more fins and tube surface area for cooling. Also, is your rad a down flow ? I've read that the cross flow rads cool better. If you have a narrow down flow, you may wanna consider modifying your set-up, so that you can run a wider cross flow, like an American Eagle, with 2 rows of 1" wide tubes. I'm not that familiar with the earlier GTO's. Don't know what is required to make one fit. But, it may be worth the effort, to get the cooling you need. 

I've read that an alum rad with 2-rows of 1" wide tubes would cool better than a 4-row. And, 2 rows of 1.25" tubes will cool even better. But the wider tube rads are pricey.

They also make 18" 7-blade flex fans, and Hayden makes a "Severe Duty" clutch, for a 7-blade clutch fan. 

https://www.amazon.com/Flex-lite-1818-Stainless-7-Blade/dp/B000CNHFOE

http://www.haydenauto.com/featured products-fan clutches and fan blades/content.aspx

https://www.amazon.com/Hayden-Automotive-2797-Premium-Clutch/dp/B000C3F3D4

http://www.ebay.com/itm/Hayden-2797...ash=item1a0c7be6b4:g:K8IAAOSwPgxVNDmc&vxp=mtr

Another option might be a GOOD 16" elec pusher fan in front of the rad. Some of these will push well over 2000cfm. That might give you the extra cooling you need.

https://www.summitracing.com/parts/flx-119/overview/


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## PontiacJim (Dec 29, 2012)

OK, the thermostat removed eliminates any restriction problems or your thermostat not fully opening and causing a restriction.

Of note to me is the fact that "When stopped and you rev it up is will cool down slightly and hold steady." This would in my opinion indicate you are not getting enough air flow through the radiator at lower RPM speeds. BUT, read to the end.

There is a parallel discussion going on about the AC fan blade that may be of interest. The owner has the 17" fan and it doesn't seem to be cooling as it should. The AC cars ran a 19 1/2" 7-bladed fan along with matching fan shroud and clutch fan. My '68 manual says the standard fan was a 4-blade 19" steel blade, 6-cyl w/AC, GTO, and 428 HO engine without/AC used 5-blade 19" variable pitch fan (flex fan). Some non-AC cars were also equipped with fan shrouds. Keep in mind that the number of blades is not as important as the pitch of the blades which draw the air through the radiator.

Some of the aftermarket flex fans don't have a good pitch or design. I went out in my shed to look at the one I was using on my 400. I bought it at Advance Auto, which seem to be an "Imperial" brand, but I looked up the part number and it appears to actually be made by Hayden. It is 19", 6 blades, and good up to a max of 6,000 RPM's. Here it is - https://www.amazon.com/Hayden-Inc-3569-Flex-Fan/dp/B000C3BB6C This thing really draws air at lower RPM's, flattens out at higher RPM's, and makes a good roaring sound that may be objectionable to some, but it worked well and I did not have a fan shroud. Looks similar to a Flex-Lite fan as well.

Next, it appears in 1968 Pontiac went to the cross-flow design radiator (along with the 19" fan) as opposed to the conventional down-flow radiator. Reason stated in the chassis manual is, "radiator offers improved cooling capabilities while making possible a lower front end silhouette due to its reduced height. The low, wide shape of the cross-flow radiator matches the grille opening more efficiently, providing greater radiator exposure and more effective cooling surface."

So, the down-flow radiator may not be as efficient as the cross-flow, but all is not lost. It would seem by your test in revving up/maintaining RPM's held the temp steady* which in my opinion *tells me that there is not enough air flow through the radiator. At this point, I would try to increase my air flow at lower idle/cruise RPM's. BUT....... it could be other, so read to the end.

Can you step up to a 19" diameter fan or is the width of the radiator core/tanks the limiting factor. If you can go larger, then I would begin here with a 19" Hayden flex fan - less the shroud at this time just to check the increased air flow. IF you are limited to the 17" diameter fan, then I would still go with the Hayden fan which can be bought at Summit here- https://www.summitracing.com/parts/hda-3565/overview/ They also have an 18" fan as well, but you may have to go with a larger opening on the fan shroud. I don't know what kind of clearances you have around the outside of the fan blades and inside of your fan shroud. May or may not work.

Something to consider & my opinion at this point. It is still possible that you have a lean condition or your timing, vacuum advance might not be right. If you are running lean, when you pick your RPM's up (and your water temp maintained), you are cracking the throttle plates in the carb and coming off the idle circuit which may be running lean when shut. You may need to richen up the idle/carb. You may be able to find a local shop that can check your air/fuel ratio at the tail pipe & check your timing/vacuum advance. Most vacuum advance cans are set for about 12" of vacuum and you may need one made for HP engines/low vacuum which seems to be more like 8" of vacuum. The Q-jet really needs to be set-up for the RAIV cam as well as your distributor/vacuum advance - all of which can cause a lean condition and put more heat into the engine. Cliff Ruggle's book on rebuilding & modifying the Q-jet shows all this in it. Here is an article on Pontiac vacuum advance - Vacuum Advance Technology - Distributor and Carburator Tuning for Pontiac Engines - High Performance Pontiac Magazine

"For peak engine performance, driveability, *idle cooling* and efficiency *in a street-driven car*, you need vacuum advance, connected to full manifold vacuum(not a ported fitting off the carb). Most stock vacuum advance cans aren’t fully-deployed until they see about 15” Hg. Manifold vacuum, so those cans don’t work very well on a modified engine; with less than 15” Hg. at a rough idle, the stock can will “dither” in and out in response to the rapidly-changing manifold vacuum, constantly varying the amount of vacuum advance, which creates an unstable idle. Modified engines with more cam that generate less than 15” Hg. of vacuum at idle need a vacuum advance can that’s fully-deployed at least 1”, preferably 2” of vacuum less than idle vacuum level so idle advance is solid and stable; the Echlin #VC-1810 advance can (about $10 at NAPA) provides the same amount of advance as the stock can (15 degrees), but is fully-deployed at only 8” of vacuum, so there is no variation in idle timing even with a stout cam."


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## thor7726 (Sep 2, 2012)

Good Evening Everyone!
We solved it! I got the car to run down the road at 180ish and when idling it stops and holds at 198ish! I’m super excited! Now comes the embarrassing part for me, (Jim you where unto this in your last post), my quadrajet idle mixture adjustments where set too lean. I set the adjustments to 1.5 turns out per the ‘generic’ instructions and never went back and adjusted them because I thought it was running so good it couldn’t be that. When my dad and I adjusted them out per the information he found, the idle smoothed out, the vacuum increased, and the car now runs and will hold steady temperature at idle. With the smaller 66 radiator and with the 66 shroud that only fits a 17” flex fan I believe I still need the 6.5” pulley and flex fan.

The engine still needs some work. We don’t think the mechanical advance is working at 100%. Total timing without vacuum advance maxes out at 26deg at 1800 rpm. I think that should go closer to 36 deg.

Its my first engine build, first quadrajet and I have learned a lot! I want to thank Dan Jensen, Jim Butler, PontiacJim, oldskool and all other GTO forum people. Also thanks to my dad for putting up with me through this engine build and teaching me so much.

We are headed to the St. Ignas car show this coming weekend in Northern Michigan. If anyone else is planning to attend look for a green 66 GTO with American racing mags and a really ‘cool’ idling 455 HO!


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## PontiacJim (Dec 29, 2012)

Ding, Ding, Ding....we have a winner! Fantastic! As you have learned, many things can affect the reason an engine runs warm/hot, not only the cooling system, but carb & ignition. All of these items have to be checked, which you did, and sometimes you have to simply replace items hoping to upgrade and solve the issue. Sometimes this works, sometimes it doesn't, but then you know what it was not and this can be a step in the right direction even if it cost you a few dollars. I hate this form of process of elimination, but sometimes with these older cars and doing it yourself (which I prefer), this is how you learn your car and all its quirks and finicky idiosyncrasies. It is how many of us "old" guys learned by hands on doing and sometimes you won, and sometimes it was big mistake.

Keep in mind that if you use any gas with ethanol in it, it will by nature run leaner than straight gas. So this means you may need to richen up the carb. You can increase idle and back out the idle screws, but be aware that you might encounter a problem when you shut the engine off - run-on or dieseling on which will harm the engine. Pontiac, and other makes, used an electric powered solenoid to raise the idle speed to around 850 RPM's when the ignition was on. When the ignition was turned off, the plunger in the solenoid retracted, closing the throttle plates and thus cutting off any air/fuel so the engine would shut off. As you increase idle using the idle screw on the side of the carb, you are opening up the throttle blades and this can allow the engine to still draw air/fuel from the carb when the ignition is turned off and allow the engine to continue to run due to the heat in the combustion chambers - which is damaging. Had a couple cars without this solenoid and I would drop the car in Drive and kill the ignition, or put it in gear if 4-speed and kill the ignition and let out the clutch to stall the engine - I didn't really know or have the knowledge at the time what was causing it so I did what worked. So keep this in mind. They do make an aftermarket solenoid you can add on just for this purpose - it'll increase your idle speed as needed and drop down when you shut your car off to close the carb throttle blades to prevent run-on.

The consensus on total timing seems to be about 34 degrees all in around 2500-2800 RPM's which is something you can play around with by changing out the springs in the distributor. This has been covered in several discussions here. I have pointed out this before as it has some good info that you will find helpful - https://www.msdperformance.com/support/set_your_timing/


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## chuckha62 (Apr 5, 2010)

26 degrees of total timing is too little. Has your distributor been changed? Has your mechanical advance been modified to restrict the throw? Getting 34-36 degrees of total will not only improve performance (noticeably!), it will also make the engine run cooler at speed (not that that was your problem).


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## Lemans guy (Oct 14, 2014)

That timing is way too retarded for that motor, will run hot. You need much more at idle and that car can take it maybe 16 degrees base, 

20 Centrifigal, and. Vac can the pulls in 10 degrees at low vac, is that an HEI distributor?

Also that seven bladed AC car fan and shroud like the gang mentioned,...but remember the fan clutch that is thermostatically controlled is the one you want...it has a little curled spring like a choke spring on the front and sets the fan clutch on when it is hot...

The straight Centrifigal one just does not cool as good...used both before.


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## Lemans guy (Oct 14, 2014)

Say 16 degrees base, + 10 from a vac can at full manifold vac gives you 26 at idle.....

20 more in Centrifigal....total mechanical will be 36....10 more from vac at light throttle cruise for 46.....

26 at idle.....and everything else you did....plus that thermostatic fan....should help you


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## BearGFR (Aug 25, 2008)

You may have done this already, but I didn't see a mention of it so...

Divider plate clearance - the plate that fits between the pump impeller and the engine. If that clearance is too wide, the pump won't work very well no matter what else you do. Lay the plate onto the water pump with no gasket between them, then use your implement of choice to work the plate until it just barely touches the impeller all the way around. When you reinstall with the gasket, the clearance will be where it needs to be. Doing that made a huge difference on my car (reasonably healthy 461 stroker - has run 11.80's at the track).

And yeah, 26 degrees total mechanical (without vacuum) is no where near enough timing. The process for finding what your car 'likes', timing wise, has been posted on here several times and would probably turn up with a search.

Bear


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## IndiangoatMike (Mar 18, 2018)

Best solution is an aluminum radiator with pusher fan if needed in stopped traffic


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