Okay. 95 Grand AM SE 2.4 quad motor. Car ran fine for about 5 - 6 months. Now the car is suddenly overheating. Thermostat replaced. No dice. Replaced thermostat again, still no dice. Car will get hot at idle, cooling fan does come on. Radiator seems to get warm on one side but not the other sometimes but not others, but I can't be sure about that. Someday's it seems the heater will affect the temp, someday's not. The coolant temp light will come on sometimes, even if the car's not into the red on the gauge. The radiator will sometimes also thud 3-6 times and sound like it is trying to get coolant or something. There was a leak on the heater core pipe that has a crossover on it back near the firewall, one end was cut shorter and re-attached this pipe will be replaced soon, however there is no leak from it right now. There is no coolant in the oil. Tonight it did not over heat when heat was left off, but did most if not all other times. I also had it idling in the driveway with heat off and it did eventually get hot after driving it. It does take a while to get warm sometimes also, but I think that's just the 25 degree weather. Anyone with any suggestions for me? Thanks in advance.

Welcome to the forum. If your radiator / cooling system has a blockage (which it sounds like it does) have the whole thing flushed and filled. I think it would be your best bet to solve your problem.

Sounds familiar.... Ok here's what my quad did when I had problems. First, it would overheat on the highway, and trying to check for air it would boil out of the tank before the fan would come on. Solution: replace clogged radiator, problem solved. Second time, got coolant in the oil, head was cracked in a bunch of places and gasket was toast. Check your heater hoses, if any of them are pinched, collapsed or blocked you will overheat as coolant goes from the water outlet into the heater core then across the thermostat. Funky design, works ok when there is nothing wrong with the cooling system. Also, if the engine cools down when running at higher revs, around 3k or more, its a heater core or hose issue as the water pump produces enough pressure at 3k rpm to force the thermostat open. Good luck.