Engine overheating at stoplights w A/C on

[emawoman]

Our 2006 Vibe does not overheat w A/C on when we are moving. However, when we stop and idle for a few minutes, the temp gauge goes up and we have to turn the A/C off or we'll overheat.

Is there a sensor that we can replace so that the engine will not overheat? It seems the cooling fan is not working at idle.

[Chiadog]

It isn't a sensor problem because the engine cooling fan is running! Sounds like the plastic fan is loose on the fan motor shaft and is not turning fast enough to move air. Once the car is moving above 20mph or so, the radiator and condenser have enough natural air flow to do all the cooling necessary. Check the cooling fan and check for dirt or restriction in the car radiator. If that is all OK, and you are certain the fan is moving a lot of air, then the radiator is likely plugged with corrosion on the inside.

[JohnO]

Does the fan turn at all? When you turn the A/C on the fan should run regardless of the engine temperature. The fan is not needed when the car is moving so if the fan breaks the symptom would be overheating when stopped. If the fan is not running, the most likely problem is the fan motor.

[Salsa Guy]

Blown head gasket comes to mind for all you issues.

[kumquat]

Check that the fan is running at full speed. Then check that your system has a sufficient amount of coolant. Then check that the serpentine belt is not loose.

If the fan is running, then it could be several things. First thing that comes to mind is a radiator or condenser clogged with debris. That happened to me once. Peer in at the radiator and condenser assemblies from the front (they are one behind the other) and see if there are leaves and dirt clogging the airpsaces.

Could also be a bad thermostat. The thermostat is a device that blocks coolant flow to the radiator until the coolant reaches a certain temperature, at which point the thermostat opens and begins allowing coolant to flow to the radiator. A common failure mode is for the thermostat to stop opening all the way, this restricting flow enough so that you can overheat when idling. Since the thermostat is an $11 part that takes about half an hour and one jug of coolant to change, that would probably be my first action if the fan and debris checks are OK.

This is GM's order of diagnosis, too:

Coolant level
Drive belt
Dirty radiator
Thermostat
Head bolt torque
Intake manifold
Head gasket
Cylinder block plug
Heater core
Coolant valve

[Salsa Guy]

With her other issues I'd say head gasket.