I have a 1988 Ford F150 that seems to be in pretty good shape all around. But I recently had the A/C Fixed. And they actually upgraded the entire system to the new kind of freon. And before I retrofited it, the old A/C wasn't working. So now that it's up and working I have been using it almost every day. And it seems to work without any problems except on the really hot days. On those days, the engine begins to overheat. It doesn't get into the red zone but when I park it I can see coolant leaking out (from the overflow, there are no leaks in the radiator) onto the ground. So what do I need to do? A friend of mine suggested I may need a different thermostat. Would that really fix this? Any suggestions would be greatly appreciated.