I drive a 2000 Cavalier with a 2.2. I'm being plagued with an overheating riddle that I can't seem to resolve. My car hasn't given me much problems until I recently replaced the radiator due to a crack in the side. After the radiator it was great for about 2 weeks until one day the temp soared for no reason. I got it home safely and found RTV stuck in my thermostat. Replaced the t-stat with a 180 Murray t-stat from Orielly's (the only one they carry). Car was undrivable and overheated immediately. Upper hose was extremely hot while lower hose was ice cold, heater however worked great . Took the new t-stat out and put it in a frying pan with water and it eventually opened but well over boiling. I physically removed the guts and put it back in holding the seal so that it was wide open. I have an adjustable temp switch on the radiator fan and set it to about 205 and checked multiple times. The car heated up to 205, fan came on, and temp dropped to about 170 when the fan cuts off, and would stay in the 170 to 205 range at idle all day. Upon driving the temp will drop to 100 due to the constant coolant circulation. All is well and it hasn't giving me a bit of issues since, except the obvious heater blowing cold due to lack of thermostat. Today I purchased another Murray 180 T-stat and put it in, and same results, coolant not circulating through the radiator. One hot hose and one cold hose. Heater works great again, temp soars and car is undrivable. Car has plenty of power, no smoke, and maintains coolant system pressure with no leaks. I made sure to bleed the air out of the system when refilling the coolant. Can it really be two brand new faulty thermostats? I'm exhausted of this stupid paradox, any suggestions are greatly appreciated,
Thanks Sean

I will keep my thoughts and questions short.If you had good heat after the radiator swap then the temperature rises I would be checking your oil cap for a milky residue for a failing head gasket.If your oil level stays normal and the oil on the cap are just oil that is a good sign.If your coolant level stays consistent that is good too.By replacing the thermostat a 2nd time would not hurt either as you did so.But now cold heat and coolant hose 1 hot,1 cold.It could be your waterpump is not circulating the coolant OR you have some trapped air in the system which COULD duplicate the issue you had.Granted new rad,thermostat and things went well for 2wks.Check the oil level and oil cap for the white goo.I am not 3rd gen savy but if it has a external waterpump or not do you hear any extra noise at idle?Your issue is puzzling as new parts,good temps,good heat and then temps rise.Unless your water pump is not working,or heater core is blocked up or even a faulty new radiator.I doubt air trapped in the system.As I am pretty tired after working on one car all afternoon I am done.

Could be a few different things I can think of.
1. The thermostats you are getting could be of poor quality. I use stant superstats from Napa or Advance. They have a small bleed hole to prevent air pockets from being trapped. I've never heard of or used Murray.
2. There is air trapped in the system. I've had stubborn cars that had to be idled with the front end jacked up and the rad cap off to burp out all the air.
3. You could have a head gasket failing or a cracked head. Combustion gases leak into the coolant passages and cause rapid overheating.

I know you said the rad was new. If you previously used an excessive amount of stop leak products that could have plugged something up.