97 Monte, 95,000 miles.

Within the last 100 miles I've done or had done:

Intake manifold gasket (it was leaking bad)
Thermostat
Water pump (old water pump looked fine)
Coolant flush/bleed

Cooling system pressure check - held pressure for 5 minutes
2x compression check - tested fine

This car keeps overheating. It will go from about 120 degrees to 240 degrees in less than 60 seconds. It will hold there for a few mins (if I can't pull over right away), then drop down just as fast. I have gone for up to 50 miles without it overheating, then the next time I started it would heat up within 5 miles. It only seems to do it once I get on the highway and go over 50mph.

When it gets hot, I get no heat until the engine cools down again, at which point I get warm air. From what I know it seems like air is getting introduced somehow but it was just flushed and bled yesterday by a professional, and since it holds pressure where would the air be getting introduced?

I am not losing any coolant that I can see. There was coolant mixing in the oil prior to the intake gasket being replaced but I don't see any now. I have taken it to 2 mechanics who both suspect the head gasket, but I don't get any white exhaust, and the car runs and drives perfectly fine.

Does anyone agree that the head gasket should be replaced? If so, considering the ONLY symptom I have is overheating, is there a more reliable way of testing the head gasket other than a compression check and looking for oil/coolant mixture?

I am also open to other ideas... I am at a loss at this point though. Thanks everyone.

Edit: Forgot to mention - at temperature I do get bubbles in the reservoir which apparently might be another sign of a blown gasket/cracked head.

 

usually if it's a head gasket, once it gets hot it stays hot. you're saying it gets hot for a little bit and then comes back down to normal? and there's no longer coolant in the oil? try putting in a cooler thermostat. if you have have a 195 now go to a 185 and see if that helps.

 

Thanks for the reply. Yes, it does cool down after staying at about 240-250 degrees for 1-3 minutes. Do you really think a 10 deg cooler thermostat would make a difference? If so, I can try it, but due to how wildly the temperature fluctuates it doesn't seem like it's just a matter of 10 degrees... I could very well be wrong though.

 

Let it overheat, bleed the system. Overheat bleed the system. If you constantly can bleed air out, i would say head gasket.

 

I will try that... I just open up the 2 bleed screws until coolant comes out right?

 

right.

once coolant starts coming out, all the air SHOULD be out of the system. So if after you bleed, and you are able to bleed again after driving for approx. 10 minutes, then there is some sort of problem that is letting air in.

To me it sounds just like what happened with my 95 lumina, and it was a headgasket. I used to overheat about 3 times driving only 8 miles to school, and I would constantly be bleeding the system.

 

Just remembered I broke off the bleed screw by the water pump... Is that easy to fix?

 

JW, how much did you pay to have your intake manifold gasket replaced?

 

I think it was about $700 w/ tax.

 

hmm bubbles generally means air...if u think about it from a physics perspective when metal gets hotter it expands. so if at cooler temps the engine is leaking coolant it will naturally get hotter and the metal will expand to fill the gap. once this gap fills the cooling system will work correctly and the engine will cool, causing the gap to reform and the engine to overheat. i cant guarantee its the head gasket but either sumtin is cracked or a gasket is leaking...best of luck