# GTO Overheats



## M.L. Blanton (Aug 17, 2020)

I have a 67 GTO that overheats. I have done everything I have read about but it still overheats. Here are the details. I have a Pontiac 400 engine that has been bored to 461 cu.in.
It has aftermarket heads, cam and valves. I am running headers and 21/2 in exhaust all the way to behind the rear wheels. It has a FI Tech EFI fuel injection system with a frame mounted electric fuel pump. The engine dyno'd at 525 HP.
I have a Cold Case 2 row aluminum radiator with dual 12" electric fans. Cold Case claims they get better cooling form the two row that they do from the 4 row' I have a Flow Kooler water pump and I gapped the backing plate to 1/32" with the gasket on the bench. Should be less than that when installed and compressed. this was not originally an AC car but I modified the lower radiator support so I could use the larger AC radiator since I have aftermarket AC. Out of desperation I also put in some Water Wetter. I'm running a 165 degree thermostat.
What else is there to do?? I'm at wits end with this car!
Lee


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## the65gto (Oct 9, 2008)

I would measure the temp using at least 2 different methods/tools if you haven't already. Is the overheating at idle or on the road??


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## M.L. Blanton (Aug 17, 2020)

The overheating occurs in traffic. I have tried three different temp gauges. It spews out coolant when the gauge gets to 245 so I know it is really overheating.


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## the65gto (Oct 9, 2008)

Assuming, that it cools down to normal temp while on the road? 
Electric fans running full speed at idle when hot
Are they sucking air thru radiator towards the engine (not blowing air thru the radiator [reversed])
Lower radiator hose has a spring in it (not collapsing)
With FI, not sure how to check air/fuel ratio. ?
Engine timing?
Shroud position/sealed
You tried 3 different gages, are these factory gauges? Due you have one of those infra red gauges to compare with

Just some random ideas??


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## BearGFR (Aug 25, 2008)

What's your ignition timing set to, both initial and total mechanical?


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## PontiacJim (Dec 29, 2012)

First, we need photos of your set-up. We might see what you do not. Give us a photo of the pulleys, belts, fan, fan shroud, radiator, and the position of the A/C condensor.

What is your idle speed? Sometimes idle speed can be too low in traffic and raising it a bit can help coolant flow. A/C should have a means to raise idle when it is turned on.

Wrong pulleys and/or ratio. If I am correct, A/C has a different ratio.

You installed the Flo-Kooler pump & clearanced - OK. IF you did the 11-bolt timing cover swap, did you install the Water Pump Bushings - Photo enclosed.

Aluminum heads should draw a lot of heat out of the engine along with the aluminum radiator. Yes, a 2-core can be better than a 4-core as long as you have the correct surface area which typically means larger tubes.

15-16 PSI radiator cap?

Purchase an inexpensive laser temperature gun. You want to know what the true temps are and not go by the gauge or the fact it pukes coolant at 245. You could have a blockage somewhere in the engine's cooling system. Shoot and record the temps of the upper hose, lower hose, manifold water crossover, and 4 places at the radiator, top left/right corners & bottom left/right corners. There will be a difference from top to bottom, but should not show a big difference from side-to-side. It is possible that in welding up the radiator, there could be welding slag or junk in it blocking some of the radiator.

As noted, what is your timing set at? Initial & total advance? A retarded timing will heat up an engine real fast.

Is your vacuum advance hooked up and working? How many extra degrees? Where is the vacuum hose connected? Vacuum advance is needed to help cool an engine down.

Not familiar with FI, but if it is running lean, like any engine, it will heat up. I know that most can be programmed, but that is out of my league.

Fans - CFM? Pusher or Puller? Shroud? 

Start with these items above and give us photos and the laser temp readings.


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## RMTZ67 (Mar 12, 2011)

Make sure your fluid in your radiator is down at least a inch....maybe 1 1/2" and not close to filled. If it still spews then, you are overheating. I thought mine was overheating because it kept spewing out when I turned the car off at 225 degrees. When I did not overfill it, it never did it again. Just a thought. Or is it spewing out while stopping at a light?


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## M.L. Blanton (Aug 17, 2020)

the65gto said:


> Assuming, that it cools down to normal temp while on the road?
> Electric fans running full speed at idle when hot
> Are they sucking air thru radiator towards the engine (not blowing air thru the radiator [reversed])
> Lower radiator hose has a spring in it (not collapsing)
> ...


Fans are pulling through the radiator. Lower radiator has a spring. I don't think it is collapsing. Air/Fuel ratio is controlled by the EFI and is set on 13.5. The engine timing is set at 18 Deg. BFTDC at idle speed and it has only a mechanical advance which gets to a max of 40 Deg.
Fan shroud is riveted to outer rails of radiator and is completely sealed. Any air that goes through the fans must come through the radiator.
All the gauges I have tried are aftermarket under dash type.
.


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## Lemans guy (Oct 14, 2014)

2 row radiator is better than a 4 row radiator?......now there is one that I never heard.

factory AC cars used a 4 row radiator, the GM engineers knewthat the condenser dumps tremendous heat load In the engine bay.

I run a 4 row US Radiator with extra large down tubes..... so it may be so....but don’t seem tight......timing is critical too retarded at idle will heat you up as Bear is asking,...shrouds ,rubber Dams around radiator and over wheels, all the things mentioned + a sticking thermostat.....even new ones can drive you nuts.

a temp gun can show you if the thermostat is even opening......on clutch fan cars too hot at idle is often a bad fan clutch that won’t pull air through the radiator......or you are doing it but A 2 core is not enough cooling.....

get that temp gun on it see the temp at the top of the fins and seethe temp at the bottom of the fins..if a down flow, if not check side to side.....if it ain’t cooling there radiator may be insufficient


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## Lemans guy (Oct 14, 2014)

If your AFR is set at 13.5 and never changes that is way too lean for power, like in acceleration, or throttle down...it should drop to 12.2 to 12.5 for power demand depending on th egasoline you use. That lean running at demand will heat up your cylinders, and it may not show until you slow down as the volume of cooling air is always less even with 2 electric fans.

since you are running a race distributor set up that is also causing heat at light throttle cruise, the idle. At 18 could take more .a but not with a dizzy and no vac advance.
Vacumn advance or computerized advance let’s you add ten more degrees of timing at cruise and idle that cannot be added with your set up.

A distributor properly curved with Vac advance and correct AFR’s will help,...alss I believe the 2 core radiator story, may be true, but I am a skeptic....

like a guy saying his4 cylinder has more torque than your 8 cylinders.......In some anecdotal
Place maybe......but in general,...uh.....no.


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## PontiacJim (Dec 29, 2012)

*Lemans guy* - "2 row radiator is better than a 4 row radiator?......now there is one that I never heard."

*PJ*: Really? _You doubt ME_?????? I thought we were friends. 

"Most modern radiators are made from aluminum. An aluminum radiator is more efficient and weighs up to one-third less than a comparable copper/brass radiator of the same dimensions. The main reason for aluminum’s greater efficiency is the ability to use wider tubes in the core. Larger tubes mean more tube-to-fin contact surface area (up to 20 percent over copper/brass), which provides better heat dissipation. That’s why an aluminum radiator with two rows of tubes can out-cool a copper/brass equivalent with four rows of tubes by as much as 30 degrees F."

From Champion Radiator:

To review our radiators:


EC Economy Core Series – *2Row – Two Rows of 3/4ths inch Tubes = Approx. 400-600+ Horsepower Cooling Capacity*
CC Champion Core Series- 3Row – Three Rows of 5/8ths inch Tubes = Approx. 600-800+ Horsepower Cooling Capacity
MC Monster Core Series – 4Row – Four Rows of 5/8ths inch Tubes = Approx. 800-1200+ Horsepower Cooling Capacity


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## Lemans guy (Oct 14, 2014)

Thanks PJ, clearly you are correct! Thanks for that clear explanation facts always rule. I did post my doubts from what cold case had told to Mr. Blanton, and you had not yet weighed in. So my skepticism was to the radiator salesman.

so if the 2 row has the necessary larger tubes and is of course aluminum, those two factors can equal a 4 row brass and copper with smaller tubes, makes sense.

Back to Mr. Blanton’s temperature,...I agree with PJ and the gang work a temp gun all over that cooling system and see what you get, and consider adjusting your AFR and getting a different dizzy. Those race dizzy’s give up a lot of lead spark and cool idling. And PS they give up no top end because your WOT has no vacumn and therefore no vacumn advance.

Some cars can run at 40 BTDC but you have to watch outfor detonation/pinging which comes from too much spark advance and or too much heat, it becomes a circle.

you have a centrifugal advance of 22 BTDC + 18 at idle. .....I would put on a proper vac can if that dizzy has a place and get 10 more degreesA set to full manifold vacumn.

Then I would set the base timing at 14 + 22 centrifugal for 36 total.

your idle timing will be 14 + 10 = 24 BTDC....an increase of 6 Degrees, which should help a little.

You can later once your cooling is fixed, see if you can test up to 38 and 40 degrees while making sure that you have no detonation.



I


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## GTO44 (Apr 11, 2016)

The real question is how much air do those electric fans move...

Not all electric fans are created equal. They should be rated at least 2,000cfm - 2,200cfm a piece. Anything under 4,000cfm total will not cool an engine like this.

Some electric fans are flat blades which are designed to be quiet. These may only pull 1,000-1,200 even being a 12” fan. The curved blades fans are the ones you want. It should like a 747 spooling up... if not than you got the wrong fans.


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## Lemans guy (Oct 14, 2014)

GTO44 analysis would stick right with your symptoms.......hot at idle.....cooler st speed


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## M.L. Blanton (Aug 17, 2020)

PontiacJim said:


> *Lemans guy* - "2 row radiator is better than a 4 row radiator?......now there is one that I never heard."
> 
> *PJ*: Really? _You doubt ME_?????? I thought we were friends.
> 
> ...





PontiacJim said:


> *Lemans guy* - "2 row radiator is better than a 4 row radiator?......now there is one that I never heard."
> 
> *PJ*: Really? _You doubt ME_?????? I thought we were friends.
> 
> ...


where does one get on of these 3 row or 4 row radiators


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## M.L. Blanton (Aug 17, 2020)

GTO44 said:


> The real question is how much air do those electric fans move...
> 
> Not all electric fans are created equal. They should be rated at least 2,000cfm - 2,200cfm a piece. Anything under 4,000cfm total will not cool an engine like this.
> 
> Some electric fans are flat blades which are designed to be quiet. These may only pull 1,000-1,200 even being a 12” fan. The curved blades fans are the ones you want. It should like a 747 spooling up... if not than you got the wrong fans.


Do you know where I can get fans of at least 2000 cam each ?


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## Researcher (Jun 29, 2020)

Derale Cooling Products 16826 Derale High-Output Dual RAD Fan and Shroud Kits | Summit Racing


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## Old Man Taylor (May 9, 2011)

Your fans have a good spec (4000 CFM). Can you tell if the fans run slower at idle than they do with the engine revved up? Those fans draw 50 amps, and that might be too much for your alternator.


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## Montreux (Mar 8, 2009)

Is the condenser spaced away from the radiator about an inch? This lets it draw more air at idle. 
Are you running A/C baffles around the radiator? Are you running an A/C pulley set (spins the water pump a little faster)? If you hold the car at fast idle, does it stay cool or cool back down? Are you running a puke tank? If no puke tank, water level should be about 1-1/2" down when cold. If running a tank, do you have the correct radiator cap? It should force coolant into the tank, and draw it back into the radiator when cold. If all else fails, GO FASTER!


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## Robert1965 (Jan 4, 2020)

Have you considered drilling a small hole in your thermostat? Has anyone here done this? I would consider it. It would cost you almost nothing to do and a simple fix.


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## lust4speed (Jul 5, 2019)

We've purchased four bad thermostats in a row that were opening very late or not fully opening, and these were both the standard and Robert Shaw type. Test the thermostat in a pan of water on the stove measuring where the thermostat starts to open and when it is fully open - might be a surprise there. Then leave the thermostat out and go for a drive and see what happens. I hope that no one repeats the Chevy wife's tale that you need a thermostat in the system to slow the water. There is absolutely no difference between no thermostat and a fully functioning thermostat. Removing it for a test allows one more item to be removed from the list of suspicious gremlins that could be causing the over heating.

I'm not a proponent of electric fans, but where they work best is at slow engine speeds where you are having your problem. A/C pulleys were roughly 8" on the crank pulley and 7" on the water pump pulley, but with a little looking the 6.5" water pump pulleys are pretty plentiful. Original systems w/o AC under-drove the pump with 7" on the bottom and 8" on the top. I added Vintage Air to my '67 and am getting by with the 15.5" radiator and the 8/6.5 pulleys and SD fan clutch driving the original 18" H.O. fan. I'm collecting parts and about ready to swap out the core support and buy the Cold Case radiator. Worse I've seen was 205° stuck in stopped bumper to bumper traffic on a 95° day, and as soon as traffic broke it went back down to 185°.


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## Dukes67 (Jun 19, 2018)

I had the same scenario with a 400 (461 stroker). I threw everything at it short of the aluminum radiator in hopes to keep it original looking. It would get hot no matter what in traffic and excessively hot in Utah summer’s while sitting at idle. It simply was lacking airflow over the radiator. I had shrouded it, gapped the fan, new fan, replaced the clutch you name it I tried it. What finally cured mine was a swap to an air conditioning pulley setup to increase the fan speed. It just simply was not pulling enough air for that big engine. I know yours is electric but I would really be suspect of either a restriction to the airflow or the fans not pulling sufficiently over that radiator.


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## mikelly2 (Nov 24, 2018)

As always lots of great info. Like most of Ya'll I'm thinking there's an air flow issue for whatever reason. If it runs cooler with the hood open at idle that would support that theory. In my experience there's typically a big difference between manufacturer's claimed CFM and what their fans actually put out.

My other thought would be a possible head gasket leak letting hot exhaust into the coolant. A hydrocarbon test of the coolant might be a good idea. AutoZone and O'Reilly's have a kit to do the test.


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## mikelly2 (Nov 24, 2018)

and another thing... In my experience higher coolant flow rate doesn't necessarily mean better cooling. If the coolant moves too fast it doesn't have enough time for optimal heat exchange.


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## M.L. Blanton (Aug 17, 2020)

Old Man Taylor said:


> Your fans have a good spec (4000 CFM). Can you tell if the fans run slower at idle than they do with the engine revved up? Those fans draw 50 amps, and that might be too much for your alternator.


These aren’t my fans. Mine are 2800 com combined. A new alternator being installed today 150 amps.


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## M.L. Blanton (Aug 17, 2020)

Robert1965 said:


> Have you considered drilling a small hole in your thermostat? Has anyone here done this? I would consider it. It would cost you almost nothing to do and a simple fix.


I have a 1/8 hole in thermostat


mikelly2 said:


> As always lots of great info. Like most of Ya'll I'm thinking there's an air flow issue for whatever reason. If it runs cooler with the hood open at idle that would support that theory. In my experience there's typically a big difference between manufacturer's claimed CFM and what their fans actually put out.
> 
> My other thought would be a possible head gasket leak letting hot exhaust into the coolant. A hydrocarbon test of the coolant might be a good idea. AutoZone and O'Reilly's have a kit to do the test.


i have the test kit and have tested. No gases in the coolant. I’m beginning to think it is an airflow issue as well.


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## M.L. Blanton (Aug 17, 2020)

Montreux said:


> Is the condenser spaced away from the radiator about an inch? This lets it draw more air at idle.
> Are you running A/C baffles around the radiator? Are you running an A/C pulley set (spins the water pump a little faster)? If you hold the car at fast idle, does it stay cool or cool back down? Are you running a puke tank? If no puke tank, water level should be about 1-1/2" down when cold. If running a tank, do you have the correct radiator cap? It should force coolant into the tank, and draw it back into the radiator when cold. If all else fails, GO FASTER!


I don’t know what you mean by AC baffles around the radiator. My fan shroud is to tied to side rails on the radiator so there is now gap anywhere. My water pump pulley is same diameter as crank pulley. I have thought about smaller water pump pulleys but have not been able to find them


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## Lemans guy (Oct 14, 2014)

I have a 4 row radiator with extra large down tubes, from US Radiator, mine is copper and brass...they make it to fit Pontiac or whatever you want they are very knowledgeable, but not cheap.

They make aluminum as well I believe and some guys prefer that.


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## Lemans guy (Oct 14, 2014)

PJ clarified very well how aluminum has real good cooling characteristics,....suffice it to say I left my draft post in the middle retuned a few hours later and finished the post. But in the meantime PJ had discussed the aluminum issue.

So you may want that advantage, if cold case says a 2 row aluminum with larger down tubes works, and PJ showed us the facts that it will, it may be as the gang says you airflow..

a clog, a stuck somewhere thermostat, like partially open, clog in the radiator, your timing and AFR as well....

stay with it you will get it....are your rubber covers in place over the wheel wells? Believe it or not it has a direct effect on airflow in the engine bay and cooling....


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## Old Man Taylor (May 9, 2011)

Just an aside - my racecar was running warmer than I liked, and took too long to cool down. I had a short factory 4 core radiator. I upgraded to a Rodney Red aluminum radiator. It made no difference at all. I changed the large single pusher electric fan to a dual pull through setup and it cooled great.


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## O52 (Jan 27, 2019)

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## GTO44 (Apr 11, 2016)

M.L. Blanton said:


> These aren’t my fans. Mine are 2800 com combined. A new alternator being installed today 150 amps.


This is the reason you’ll never fully cool that bad boy even with perfect AFR, perfect timing and a bitchin aluminum radiator.

As stated, You need to upgrade your fans. I like to see 2000-2200 cfm per fan. Like i said before it needs to be 4,000cfm or more to move the amount of air that is needed to properly cool these motors. Derale is good and so are some other manufactures like cold case. My favorite is the Flex-a-lite Direct fit dual 13” fans with shroud. It wont fit in some cars and needs modifying to fit others but at 4,400cfm and really nice sealed deep shroud, it gets the job done even on the hottest days.


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## tomwadsworth (Sep 30, 2018)

I’ve been dealing with a similar problem. I’ve Had overheating Issues for 3 years and done everything imaginable, except a fan assisted oil cooler. When I was looking for a new a/c condenser I spoke with a rep from One of the after market suppliers. He said I needed to relocate my fans to push air through the new condenser. He also mentioned a clutch fan. Made by Hayden, “severe duty.”. Since I have made those changes, my overheating is not completely gone but it is much better. I’m going with higher fans when I can. At least 2000 fans each. I think that will do it.


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## M.L. Blanton (Aug 17, 2020)

tomwadsworth said:


> I’ve been dealing with a similar problem. I’ve Had overheating Issues for 3 years and done everything imaginable, except a fan assisted oil cooler. When I was looking for a new a/c condenser I spoke with a rep from One of the after market suppliers. He said I needed to relocate my fans to push air through the new condenser. He also mentioned a clutch fan. Made by Hayden, “severe duty.”. Since I have made those changes, my overheating is not completely gone but it is much better. I’m going with higher fans when I can. At least 2000 fans each. I think that will do it.


Did you actually relocate your fans and make them pusher fans?


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## Montreux (Mar 8, 2009)

M.L. Blanton said:


> I don’t know what you mean by AC baffles around the radiator. My fan shroud is to tied to side rails on the radiator so there is now gap anywhere. My water pump pulley is same diameter as crank pulley. I have thought about smaller water pump pulleys but have not been able to find them


Ames P168 1966-67 AIR CONDITIONING SEAL KIT (12 PIECES) WITHOUT PUSH PINS (RE) 
This kit seals the radiator to the radiator support so that air from the hot side can't get back to the front of the radiator. There are also pieces that seal the bumper to the radiator support, so that all air that comes through the grill goes through the radiator, BUT those pieces require metal pieces that attach to the radiator support and support the rubber pieces. As far as I know, these are not being reproduced.


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## vettvet (Oct 17, 2013)

M.L. Blanton said:


> The overheating occurs in traffic. I have tried three different temp gauges. It spews out coolant when the gauge gets to 245 so I know it is really overheating.


If i might ask, what did you do for the oil filter setup on the new motor? Is it still the original canister type or did you use a spin-on?


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