97 cavalier 2.2 overheating

my 97 cavalier with 125K on it began overheating when I installed a thermostat. I bought the car from an auction, and it did not get past 100 degrees due to no thermostat in it. I have replaced the thermostat x 3, new water pump, flushed the coolant system, checked all hoses and clamps which are fine, have the right amount of coolant in system and have bled it x 3 for air bubbles. Now the car will overheat when at idle after driving for 20+ minutes. The radiator fan comes on half of the time. No cracks in block or in head. Oil and coolant look and smell fine. No smoke. Where should I go next??

no insult intended..did you put the thermostat in upside down??

also my 2 cents...buying from an auction you probably have no service history and could be thermostat was removed to create better flow because someone put some junk in the system to fix head leak(know issue for these engines)..just a thought

yes, thermostats are in correctly and seem to be working, heat blows out hot. Just did a compression check and is all fine. Replacing the ECT sensor but can't think of anything else to do!!

check for blocked radiator core or something plugged up restricting flow....
also is the cap holding pressure, sometimes it's that simple but easily overlooked

With the bad thermostat in it, the car will not get above 100 degrees, so it seems to be flowing fine. Drained the radiator last night, and there was about 1.5 gallons in it. Would a blockage still remain if flushed system 2 different times? Nothing is coming out of cap, could it still be bad? All hoses get hot, heater blows hot, fan does kick on but isn't enough to cool off engine. After all this last night, it still got hot at idle. Thanks for you help, this is killing me!!

yes,blockage can still be there after a flush.alot of that crap that says is safe to put in the radiator hardens up and blocks flow or just lack of flushing system can create build-up....if the seal on the cap has any indication of wear it should be replaced...it does not have to be leaking fluid out..could be just small leak of pressure

can you tell if thermostat is opening??...you should be able to feel pressure on top hose if it is open and there is good flow...

your cap is on the tank? or can you see in the radiator?

didn't you say when it won't go past 100 it is with no thermostat in it?...is it no termo or bad thermo?

OK so now we replaced the relay to the radiator fan, and so far it is not overheating. Also replaced the cap on the tank, and bled again. The thermo in now is opening up, I think, because upper and lower hoses get hot and have pressure. Without the thermo in it stays cold. I bought some stop leak for raidator because I am out of ideas, but can't see any visible leaks.

hope that works for ya,do not use stop leak if there are no leaks visible