98 Grand Prix overheats

My '98 Grand Prix is starting to overheat. When I got the car last spring and on through the summer the temperature seemed to be pretty stable no matter if it was hot weather and the A/C was on or off. According to the Dash temp. guage, the temp was staying between 190 and 200.

Last fall I changed the coolant (used Dexcool) and the themostat (190).

I live in PA. We have had a lot of cold weather. Recently we had a warm streak and I saw the temp start creeping and go over 210 on the guage.. the fans would kick on and the temp goes pretty quickly back down to 185 - 190.

Car seems to stay pretty cool during cold weather like it should.

I don't appear to be missing any coolant. I suspected that at first. I haven't double checked yet for an "air bubble" by the thermostat. Probably ought to do that first.

My 2nd car is a 97 GTP. I am contemplating switching the fan relays (2) between both cars to see if that made a difference. I suspect it won't. Maybe I have a coolant temperature sensor going bad?

Thanks in advance for any thoughts. :-()

I doubt you have an air bubble in the system since you have run it for so long and the problem is just happening now. When you changed the thermostat, did you change the hoses? It is possible that the hoses are going bad and restricting flow. I would also doubt that the problem is with the temp sensor since the fan sensor is seperate and works on the coolant temp as well. I would suspect that the thermostat is going bad again. I would change it again and replace the hoses. If it continues to overheat you may have bigger problems such as a bad head gasket or a plugged cooling system.

I agree with GTP, and would replace the T-stat and any hoses that look questionable.