Thermostat question


car is 2001 Chev Malibu, 6 cyl-

Besides over heating, will a stuck, closed thermostat cause water/coolant to boil out of the resevouir? Can it cause air pockets in the coolant system?

Thank you.




If the radiator cap has failed, even a good engine cooling system will boil over. The simplest test is to change the radiator cap. If the coolant doesn’t boil over into the over-flow bottle, then, it may be ok. Are you going by the dash mounted engine temperature gauge?

Typo error. Make that a radiator cap.


although there may be other opinions differing:

in order of cheap to $$$

change the radiator cap.

change the thermostat.

check water pump circulation.

just so you know. typically a t stat does NOT break closed. they almost always break open.

you can remove the t stat and reassemble the thermostat housing with NO tstat. start the engine with the radiator cap off. look inside the radiator for flow. if there is no flow the water pump is shot.

if there is flow, then install a new t stat, and then check the temp.


HOW BOUT FREE!!! press check cooling the fan working no tools needed.


Thank you all for your answers-I anticipate a head gasket leak but was trying to explore any other possibilities-


well, in truth it sounds like you may indeed have a head gasket leak, but before you do the 600 dollar repair, do the cheap stuff first.


will definitely try the cheap stuff first- thanks again.


that thermostat is a bear to change it is located behind the exhaust cross-over pipe good luck. this car doesnt have an over flow tank like some are thinking of it has what is called a surge tank and your radiator cap is actually on the surge tank you do not physically have a cap on the radiator itself. hate to rain on your parade but i dont think it will be something simple hope i am wrong for your sake.


You could save yourself so much wonder, and work, and guess-changing the wrong parts if you got the repair manual and went by it; or, took it to a shop to diagnose it. After they diagnosed it, you could, still, change the defective parts they find.


when not changed properly they can do more damage than good and then the cryn begins


It can’t cause air pockets unless the coolant boils. Steam is like an air pocket. It can cause coolant to boil away out of the reservoir. Once the coolant boils, you can have an air in the block somewhere or in the heater core.




Any decent repair shop can “sniff” your coolant tank with a device that can detect any hydrocarbon (gasoline) vapors present. If hydocarbons are detected, you have a combustion gas leak into the cooling system, not a failed thermostat. Also, a blown head gasket will pressurize the system and blow coolant out even when the engine is cool, depending how bad the leak is.