Mine also over heats but I hit some bumps that sent me flying and the mustang trannys cooling lines flat, I've replaced everything over hauled the motor, no one believes me but I think it's the water ports blocked by debri ,over heats high and low idle around town on the freeway, within 15miles or 20min, It was that day that I hit the bumps that it started, I know the ports use to be smaller for distance. Anyways that's what I think.