96 Lumina - Heater / Over-heating Problems

Here is a strange one... concerning an intermittent overheating and heater problem.

96 Chevy Lumina.. 3.1L

After having driven for a while (warmed up to normal temperature) the heater starts to blow cold air and the Engine Temp. Guage rises to the 3/4 point. If you turn the heater to the off / cold position. The engine temp drops back to normal and heater once again blows warm air.

Took it to a radiator specialist where they could not duplicate the problem (ie: ran the engine for an hour with no over heating). The drained the system, filled and bleed the air out of the system.

Worked fine for a couple of days then the evil cycle returned.

Still a trapped air problem or something else.

Thanks

I have the same exact problem with my 97 buick century 3.1 motor My mechanic just did the intake gasket flushed out radiator and changed oil. He was burnt on this one. It did nothing to solve problem and is now showing c/o Readings in the radiator. He is now about to tear it down to remove heads and new gaskets plane if necessary. I hope this does the trick. I have 112k miles on this car have only owned it a year for golf runs with buddys and overall beater, but I love the comfortable ride it gives. Checking online I see this is a very common problem with these m,otors and it is usally the intake gaskets, but I guess I couldn't be so lucky I have to dig deeper. Best of luck with yours. :banghead:

I have the same exact problem with my 97 buick century 3.1 motor My mechanic just did the intake gasket flushed out radiator and changed oil. He was burnt on this one. It did nothing to solve problem and is now showing c/o Readings in the radiator. He is now about to tear it down to remove heads and new gaskets plane if necessary. I hope this does the trick. I have 112k miles on this car have only owned it a year for golf runs with buddys and overall beater, but I love the comfortable ride it gives. Checking online I see this is a very common problem with these m,otors and it is usally the intake gaskets, but I guess I couldn't be so lucky I have to dig deeper. Best of luck with yours. :banghead:
I was gonna say, that sounds like a small compression leak, forming an air pocket in the system. The symptom sounds typical of air in the system, but if it returned in a couple of days, without an external coolant leak, the head gasket is likely the problem. The intake gasket leak won't allow air to form in the system. The gas analyzer reading at the radiator cap pretty much nails it. There used to be a neat little clear cylinder full of fluid you put on the radiator neck, and fill it above the neck, so you could watch as the little bubbles from compression formed, leaving no doubt. Haven't seen one of those in a while. Sometimes you can hold the throttle at about 2500 RPM with the engine fully warmed up, and watch the bubbles blow back through the overflow into the resevoir. It may take a few minutes for them to start blowing back. Try it with the radiator cap loosened one notch and see what it does.

Thanks to you both for the insight.

The garage think's it might be the intake gasket as it has some signs of weepage and put a 7lb. rad. cap to extent it's life. Good to know that air can not be sucked in via the intake gasket.

Squeezed the hoses and air bubble back into the reservoir. Either they didn't get all of the air out of the system or it's getting in like you suggested though a compression leak.

Have read that it's mighty difficult to get all the air out of this engine take up to 5x tries. Truly evident in the fact that it has (2) bleeder valves.

Will purge the air again and try your suggestion to look for bubble generation in the resevoir before taking it in for a formal gas analyser reading.

Will keep you posted on the res

Problem found on my motor. It was the back head gasket head warped. The heads are being planed and put back together and I should be good to go for another 100k :biggrin: