I have a 1991 Camaro RS 305 TBI. It had an overheating problem, bad radiator and hoses. Replaced the radiator, and hoses, and the thermostat to be safe. For a day and a half it was fine. Then sitting in traffic it overheated again. (It's about 115 out right now. ) So today, I drove it and it started to overheat this morning on the highway. Never happened on the highway before. I turned on the heater and the temp came right back down. On the way home with the heater on, it was ok.

Also when the car does get too warm, it won't start again for about two hours. Not that it won't catch, the starter is just dead, well past the time the coolant has cooled back down. Bad starter? And do you think the overheating with the heat off is maybe a defective thermostat?

Air dam is in good shape.

Thanks,
Bryan

 

Usually, if you are overheating on the highway the air dam is not doing so well.

Have you made sure that the fan turns on at 215-225 degrees?? Also, have you flushed the whole system??

Its a bit puzzling that once you turn on the heater it cools down. There could possibly be a problem with miss-routed hoses which in return don't flow the correct way to correct places untill they go through the heater core (when you turn the heat on). I would check into that.

Stil, thermostats are usually designed to get stuck open, however I've had them not open at all. So, its worth checking, but I am not sure if thats the problem since you do get cooled down.

Misrouted hoses sound like something to check out.

Also, look at that damn air dam. They need to be replaced especially if its still the stock one. Its one of those things I look to replace when I buy the car. Unless they function properly...

Good luck.