Overheating issue =-(

[Stephen Bernier]

Hi everyone!
I'm on my second Grand Prix...been pretty happy with both!

I am having issues with a 98 GTP that i own. It has 175k on it...still feels pretty strong!
My car starts to over heat when it is sitting at idle. When i drive the temp is normal. When it starts to overheat at Idle and i turn the heat on and rev to like 2k rpm...the temp goes down to normal.

I have checked the radiator fans and they do kick on..both of them. I Just replaced the thermostat and that didn't help.
Any ideas?

[theaceofspades]

Still have dex cool in the system? Or possibly air after replacing the stat.

[3800 Man]

Are you losing a lot of fluid? Not as confident in it fitting your symptoms but you might check the coolant elbow for a leak.... Very very common

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[Sven the Sexman]

My guess is air in the system. Follow the bleed procedure that I'm positive Scotty will post momentarily.

[Scottydoggs]

to bleed the air out, let it idle rad cap off till the fans turn on, (when the fans are on the temp is over 195 deg, the t stat is wide open) then open the bleeder screw on top the t stat housing a few turns till a steady stream of coolant comes out the hole, shut the screw, top off the rad. cap it

[Stephen Bernier]

Thanks for the quick responses guys! i appreciate the help! my gf is pissed at me because it overheated when she was stuck in highway traffic...So i am in the doghouse. After i replaced the thermostat i didn't bleed it. I will look up directions to do that.

As far as the coolent, it is a green color put in by the previous owner. Is it possible that i may need new coolant? If i needed new coolant wouldn't it overheat while driving?

My coolant level is good and i dont seem to be leaking anything!

[Sven the Sexman]

See Scotty's above post.

[theaceofspades]

Scotty always chimes in lol and provides a solid answer

[Stephen Bernier]

ok, so i went out to bleed it...when i bleed it, i don't ever get a steady stream...it is only for a few seconds and is mostly steam. The engine never cools down and just keeps starting to overheat.
I tried to bleed it for about 15 minutes, how long should something like this take?

[Scottydoggs]

it can take up to 15 minutes for the fans to come on at idle.

sounds like maybe the t stat is bad and not opening up. its worth checking and changing, they dont cost much.

worst case the water pump is shot, like rotted impeller, or the rad is clogged up.

[Sven the Sexman]

It's definitely airbound. Remove thermostat housing and thermostat. Fill engine with coolant through the LIM until it comes out the upper rad hose. Reinstall all components. top off and drive.

[Stephen Bernier]

Sven,
I was going to try what you recommended here in a few minutes...i had the hood open and wanted to ask a question before i got started.
The overflow tank has a cap on it with a circle on the bottom side of the cap. Should there be a straw from the cap to the fluid?
I do not have one, could this cause air to get into my coolant system?

[Stephen Bernier]

Scotty,
I already replaced the tstat. Wouldn't the things you recommended cause the car to overheat even while i was driving it?

[Sven the Sexman]

Sven,
I was going to try what you recommended here in a few minutes...i had the hood open and wanted to ask a question before i got started.
The overflow tank has a cap on it with a circle on the bottom side of the cap. Should there be a straw from the cap to the fluid?
I do not have one, could this cause air to get into my coolant system?

Yes. The overflow hose should go to the top of the reservoir cap from the radiator and there should be a hose in the bottle. The hose may be stuck in the reservoir or you can just put a hose on there. Then basically you need to makes sure the reservoir is filled to its proper level and bleed the system as explained.

[Scottydoggs]

Scotty,
I already replaced the tstat. Wouldn't the things you recommended cause the car to overheat even while i was driving it?

t stat are bad brand new sometimes, it happens.

that over flow tank hose missing is not the problem tho.

take the t stat back out, leave it out. see if it over heats at idle, if not the t stat is bad.

[Sven the Sexman]

t stat are bad brand new sometimes, it happens.

that over flow tank hose missing is not the problem tho.

take the t stat back out, leave it out. see if it over heats at idle, if not the t stat is bad.

It kinda is a problem Scotty, however it won't be the entire problem. when the coolant expands due to heat, it goes into the overflow. Then as the vehicle cools down, the coolant contracts resulting in a vacuum being formed in the cooling system resulting in coolant being drawn from the reservoir. If it sucks air into the cooling system, it can cause this all to happen all over again.

[Scottydoggs]

i hear ya, but it wont over heat from it at idle from a cold start, thats just silly.

and he would be leaking coolant with no tank. or no hose to it. hmmm hmm eh eh lol

[Sven the Sexman]

i hear ya, but it wont over heat from it at idle from a cold start, thats just silly.

and he would be leaking coolant with no tank. or no hose to it. hmmm hmm eh eh lol

97-98 GP used the stupid reservoir on the D/S of the car near the airbox. it had a hose that runs to the top of the cap then one that runs from the cap down into the coolant. And if it sucked in the air when the coolant contracts, the air pocket is going to get stuck in the top of the rad, the T-stat, or the heater.

[Scottydoggs]

i know what your saying, but at the same time wheres the hot coolant going? the over fill should be full by this tube missing in the tank.

guy said it dont leak and is full.

im calling scooby doo and the mystery machine to come solve this one.

[jeepmanwv]

If you have already replaced the t-stat and the fans are working I would say the water pump is shot. It might not be leaking but the impellers are prob rotted off.