# 69 gto 400 overheating - need help!



## jwgto (Dec 30, 2008)

hello

I just rebuilt engine in my 69 gto. It ran fine before I rebuilt it but it had a spun bearing so i decided to rebuild the whole engine. The first time I started it up it got pretty hot. I assumed it was the factory waterpump so i replaced it with a high performance pump and installed a temp guage. I then started it again and it got up to about 210 degrees so i shut it off. The hose going from the bottom of the radiator to the water pump was cold and the one going from the thermostat to the top of the radiator was hot. The radiator was hot where the hose was going into the top but the rest of the radiator was cold. It seams that the water is not pumping. The radiator is a brand new 4 core aluminum so i dont think it is plugged. I have edelbrock heads but I used the factory intake manifold. The compression ratio is about 10:1. Also the hoses going to and from the heater core were very hot. If you have any suggestion please let me know! Thanks


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## Rukee (Feb 8, 2007)

jwgto said:


> hello
> 
> I just rebuilt engine in my 69 gto. It ran fine before I rebuilt it but it had a spun bearing so i decided to rebuild the whole engine. The first time I started it up it got pretty hot. I assumed it was the factory waterpump so i replaced it with a high performance pump and installed a temp guage. I then started it again and it got up to about 210 degrees so i shut it off. The hose going from the bottom of the radiator to the water pump was cold and the one going from the thermostat to the top of the radiator was hot. The radiator was hot where the hose was going into the top but the rest of the radiator was cold. It seams that the water is not pumping. The radiator is a brand new 4 core aluminum so i dont think it is plugged. I have edelbrock heads but I used the factory intake manifold. The compression ratio is about 10:1. Also the hoses going to and from the heater core were very hot. If you have any suggestion please let me know! Thanks


Welcome to the forums.
If you have a 195* thermostat then 210* would not be excessive. I would let it run longer and see what you get. You would be safe running it till about 250* if you needed to to get the thermostat to open, burp the air out and get everything flowing properly. Leave the radiator cap off until you can see the antifreeze flowing and the upper hose is hot. Once you do, rev the motor slightly, refill the radiator while it's reving then put the cap back on before you let of the gas. It should be good to go.


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## geeteeohguy (Feb 2, 2008)

210 is a pretty normal temperature for a Pontiac. Mine have run at 210-215 for the past 30 years.....If the water exiting the engine at the T stat and entering the rad at the top tank is HOT, and the water at the lower tank/hose is COLD, it means you have an EXCELLENT radiator that's doing it's job: it's losing the heat!
Jeff


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## jwgto (Dec 30, 2008)

thanks for the feedback. I have a 180* thermostate. What concerned me was the temperature was climing pretty fast and I couldnt feel the water flowing through the hoses. I will take off the radiator cap and give it another try tonight or tommorrow and see how it works.


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## geeteeohguy (Feb 2, 2008)

Run a 160 stat and with the cap off, engine cold, start it up and wait for it to open. After it warms up, you should see water flow pretty easily. You can use a meat thermometer or a pyrometer to verify that your guage is accurate. I drove an "overheating" GTO for over ten years until I fixed a bad dashboard ground circuit.....my temp went from 245 to 195 just like THAT!


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## jwgto (Dec 30, 2008)

last night a put in a 160* thermostat and ran it with the cap off of the radiator. As soon as it got to 160 degrees the water started circulating and it never got hoter than 160! I think that is a little cold so I might try putting the 180* thermostat back in and see what happens

Thanks for everybodies help!


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## Rukee (Feb 8, 2007)

:agree
Anytime!!


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## jetstang (Nov 5, 2008)

160 degree stat is great as long as you don't need heat. I run them down here in FL all the time, summer is fine, winter is a little chilly. Also, I drill a pin hole in the stat to allow the engine to bleed so you don't have to wait for the stat to open to bleed the system.


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