Mystery Overheater

I have a 1997 Chevy Cavalier. Recently, it started leaking fluid from the water pump. I drove it on low fluid for a few days before figuring it out, but it didn’t overheat during that time. After refilling the coolant, the car started overheating–even while idling! (I’ve never driven the car for more than ~10seconds when it overheated) I’ve replaced the water pump, coolant cap, and the thermometer, but it still overheats. The strange thing is that is DOES NOT overheat when the thermometer is removed completely! My mechanic is stumped. I’m a poor college student and can’t pay for him to dink around with it anymore. Please help?

When you refilled the coolant did you refill the reservior or the radiator? I don’t know about your specific system but if you opened the radiator sometimes the cooling system needs to have air bled out of it. Otherwise it overheats.

I suspect you mean it doesn’t overheat when the (thermostat) is removed and if it seemed to boil over after only 10 seconds running it wasn’t overheated but has a bad issue with compression in the cooling system, which I hope is not the case.

Think about what you’ve writen here. It is a thermostat problem. The thermostat is in upside down. Different makes of cars will have different thermostats, but they work on the same principle - I can’t tell you which way is right-side-up. You’ll have to try it both ways. And, it is not uncommon to have to refill the radiator after it has overheated and you have replaced fluid recently. Some of it will boil off and as you drive it air pockets will circulate to the radiator Like it is supposed to)