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Overheating & no heat

12-03-2010, 01:35 PM
Can someone help?

My 2000 Grand Prix is overheating and does not blow any warm/hot air from the vents when it starts to overheat.

Coolant level is good.
Changed the Thermostat.
Changed the LIM gasket.
Pressure tested the coolant system and no pressure loss (no leaks).
Water pump was changed a little over a year ago.
When the engine is warm all the hoses are warm except the couple attached to the heater core.

The odd thing is, is occasionally the vents will put out warm air. When this happens the car does not overheat but when the air (while still on hot) turns cold the engine overheats very quickly.

I'm thinking there could be a clog in the system possibly.

Since the coolant system doesn't lose any pressure when testing it I don't think it's a head gasket.

Could a bad heater core do this?

12-03-2010, 01:41 PM
It sounds like you have air trapped in the cooling system. This is a common issue on many GM FWD cars. First off, what engine do you have in this car?

12-03-2010, 02:11 PM
It's a 3.1 engine.

I've let the engine run with the radiator cap off to get rid of some of the air (lots of bubbles) and also have opened the bleeder valve to release some air. Did both for about a half hour a piece just to make sure.

The bleeder valve is just releasing coolant now. It could still have some air though. It doesn't make sense how the tubes to the heater core are higher than the bleeder valves and the radiator cap.

12-03-2010, 03:41 PM
The best way to bleed the air out of these cars is to jack the right front corner up high enough so the radiator cap is higher than the heater core, then do your bleed proceedure.

12-03-2010, 04:00 PM
Thanks for the tip.

I'll try it out tomorrow morning and let reply after the results.

Hopefully this resolves everything.

12-04-2010, 09:46 AM
When you tried bleeding it with the rad cap off, how much air came out? And was there little bubbles?

When did this overheating issue start happening? Immediatly after you changed the LIM gaskets?

Possible it has a bad head gasket.

12-04-2010, 01:46 PM
The car overheated a few weeks ago. This is what I've done in order.

Then changed the thermostat - didn't help
Tried getting rid of air in the system - didn't help

Noticed some coolant on the side of the engine
Changed LIM Gasket - didn't help
Tried getting rid of air - didn't help

Borrowed a coolant pressure tester
No pressure loss with plugs in
Took plugs out and still no pressure loss (gaskets holding 20psi)

Jacked up car and tried getting rid of air - didn't help
Took off water pump which is in good condition

Thinking of getting the coolant flushed tomorrow.

[edit] when leaving off the radiator cap there was a lot of little bubbles as well as a large one occasionally. Left the cap off till the bubbles stopped.

12-04-2010, 05:59 PM
Possible it has a bad head gasket.


Common problem with the GM 3100/3400 60 degree V6 engines. Run a compression test.

12-05-2010, 02:00 PM
Yesterday took out all the spark plugs and did a pressure test on the coolant system. No loss in pressure.

What other ways is there to see if it is a head gasket issue?

Hopefully it isn't. :banghead:

12-05-2010, 04:03 PM
If no loss in pressure test - Test Passed
Was this test done Hot, or cold?

If there's an air pocket near the thermostat, it might not open!
you might need a garden hose to force a little more water pressure through the system!
When cold, take the extra coolant out of coolant reservoir with a Turkey baster. , probably has a coolant bleed procedure.

12-06-2010, 01:16 AM
Tomorrow going to borrow a block tester. Some friends keep thinking its a head gasket and I figure I might as well check it out. I've never used one before.

The car is still having issues. Haven't flushed the system yet probably will in the next few days.

Today we topped off the system by taking off a high point hose (going into the heater core) and filled it there. Blowing pressure into this hose does circulate the coolant through the system.

[edit] the pressure tests were done when the engine was cold. I did today hook up the pressure tester and then started the car. Pressure did rise to about 20 psi (thermostat was still closed) then I turned off the car and it didn't lose pressure after about 5 minutes.

12-06-2010, 09:38 AM
What other ways is there to see if it is a head gasket issue?

The best way is to do a cylinder leakdown test. Although many of us do not have the tester nor an air compressor to use.

Like Bob stated, a compression test should give you an idea.

The reason pressure testing the coolant system wont always work to check head gaskets is because the cooling system only gets 16-18psi. Combustion pressures can reash 100 psi or higher. A head gasket could hold 20psi but might not hold 100psi.

Another way to tell is to start your car when its cold. Immediatly after you start it get out and grab a radiator hose. If its cold and has pressure built up immediatly, its getting combustion gasses leaked in.

12-07-2010, 07:07 PM
Nothing new. Burped the system for over an hour today and warm air actually started coming out of the vents the temperature was stable for once...then I took it for a drive.

It overheated after driving it for roughly two miles.

Tomorrow a compression test on the cylinders. I almost want it to be a head gasket just so I can finally blame it on something. Haha

12-07-2010, 10:26 PM
Have your catalytic converters checked?

A plugged catalytic converter could over heat, and the loss of your coolant and heat.

The test is cheap, and you can rule them out!

12-12-2010, 03:04 PM
Just finished a cylider leakage test.

They are all registering between 14% to 25%.

Still have no idea whats wrong.

12-15-2010, 10:28 AM
When you did the leakage test, did you open the radiator cap to see if bubbles were escaping?

12-15-2010, 01:35 PM
It is a head gasket. :eek7:

On one cylider. Going to try that Bar's Leak stuff. Hopefully it'll last until it warms up so I can replace it.

12-18-2010, 09:13 AM
Sorry to hear that. Make sure to replace the head bolts when you have the heads off.

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