my car was overheating, but the overheating didn't went into red zone. slightly above the normal range and there was coolant leak on the day happened.

Next day, I checked with mechanic to see if leaks there. They pressure tested and don't find any leaks.

After they returned the car, again everything seems normal(driven for 4 days).
seems thermostat is sticky. I bought a thermostat just in case if problem repeats.

Background:
First time I observed, I was on highway and it's cold (40 F)outside and my a/c is in auto mode. In a/c auto mode, a/c is still throwing cold air. I switched to a/c econ mode, switched on leather seat heat buttons(both driver & passenger). After few mins, I observed overheating problem(though it didn't went into red zone). I turned off leather seat buttons and a/c. then it came to normal.

Second time I observed, the following day after few miles driven with a/c/heaters all off.

After mechanic returned car, no issue observed.

I'm wondering, is the problem just with thermostat or anything else?

Thanks

 

Same thing happened to my 04 coupe. Radiator started leaking massive amounts of fluid EVERYWHERE ( the fan would spray it over engine compartment and belts) so i couldnt find the problem, after getting a new radiator everything was perfectly normal, no leaks, no overheating. Installed it myself and was good to go that same day! Perfect chance for a coolant flush lol