car would heat up because of exhaust system

The car would heat up. The radiator would coolant somehow, I would have to refill it. Not a huge problem. But the car would heat up so much that the fan would be turned on even after the car was shut off. I'm guessing there was a fix, I took it to a mechanic once and he changed the radiator cap or something, but that didn't fix the problem. Sometimes the temperature would go all the way to hot. In the winter it would be fine. In the end it stopped having that issue though somehow, I sold it, and later on found similar issues given by consumers on Edmunds.