Overheating buick

My niece has a 2005 Buick Rendezvous. It is overheating. Her brother changed the thermostat and this didnot seem to help, In addition, he looked at the water pump and didnt see anything. However, he did say that, anytime he ran the car and then opened up the radiator, he had to let air escape. I have never hear anything like this in all the cars that I have had. Does anyone have any suggestions about what the issue might be? I don’t have any other information about this but can probably find out, if you need more.

Thank you in advance for your kind, thoughtful answers.

With the engine cold, have the brother remove the cap and start the engine.

While the engine idles he should watch the coolant. If bubbles appear in the coolant, it indicates a blown head gasket.


deteriorated intake gaskets . . .

always a possibility, with an older gm

Check the dipstick for a milky/creamy color if it is so then that’s a blown head gasket. Another indication is white pummels of smoke out the exhaust. However, this time of year it’s hard to tell for the latter.


You’re not entirely correct

“milky/creamy” color could also be indicative of failed intake gaskets, which can allow oil and coolant to mix, depending on the engine design

Pressure buildup in the cooling system is normal and there will be a release of air, and maybe coolant, when the cap is released on an engine that has been running; unless there’s a leak of some size.

What about cooling fan operation?
Overheating in town, on the highway, or both? Those answers could help to formulate a wild guess… :smile:

OK4450, did you mean to say there will NOT be a release of air when the cap is released?

Air should have no opportunity to enter a properly purged and sealed cooling system. Any left after purging should go past the cap and bubble out the reservoir, and the withdrawal normal with contraction due to cooling should be pure coolant, drawn from the reservoir.

No. There will be a small, maybe even tiny, amount of air in the cooling system and once the coolant starts heating up or at some point while it’s cooling down that small amount of air will be under pressure. Release the cap and there will be a whoosh to some degree.

My Lincoln for example has a 1" air space in the coolant bottle with a cold mark. At full operating temps that airspace is almost gone. During warmup or engine cool down pressure will build and whoosh out the cap when loosened. Same for the Merkur, the SAAB, and even my daughter’s Mustang.

This is more true on vehicles with pressurized coolant bottles instead of overflow bottles.