Bought the car 3 months ago with 116k miles. Had the radiator flushed and refilled because of previous experience with cars that weren't driven much in the past. After that the car ran hot on me after driving about 70 mph for about 50 miles. Gauge went to 3/4 but never overheated. Took it in the next morning and had.a thermostat put in. After that, while driving around town for about 20 min, gauge would read up to 3/4 but go back to 1/2 after stopping at a light or driving faster for a few miles. Next was about a month later, drove from work and made it about 1 1/2 mi before it overheated (got overheat msg on display). Pulled over and had.it towed to same shop. They said belt that turned water pump had shredded and replaced it and the tensioner on water pump. Same issues existed regarding driving for 20 min & going over half and.then.back down. Took it back to have pressure test done to rule out head gasket, told no leaks, everything working how it is supposed to. Next time I was on the interstate for extended period at freeway speeds it overheated again. Had it towed back to town, had a mechanical tell me head gasket was blown. He said the reason was bc it said cylinder 1 misfire in the computer so that meant coolant was fouling the plugs causing misfire. I got a 2nd opinion. Plugs were not wet, not coated in white, getting fire, no coolant is leaking or needing to be added, no coolant in the oil, no oil in the coolant, not smoking. He said head gasket was not blown. Suggested simply getting a new cap for the reservoir. So I did and it does a lot better in that it doesn't seem to go past half near as easy, but on the highway it does. I am so frustrated and don't have time or money to continue taking.it here and there. Does anyone have any idea what could be.going on???? Please help!