Q: Engine overheating gmc Yukon xl with ac on. Already replaced head gaskets, thermostat, flushed system. Good on correct coolant.

Hi Laci. Thanks for contacting us today. When the AC is turned on, it will create more strain put on the engine, causing existing small problems to accelerate. There are a few things that could be causing this problem such as a clogged heater core or other obstruction of coolant, air bubbles in the coolant lines, a malfunctioning cooling fan, or even a damaged coolant temperature sensor. It’s also conceivable that the original overheating episode that most likely damaged the head gasket may have caused the cylinder head to warp slightly or cause other internal engine damage. To know for certain, you should have a professional mechanic come to your location to complete an overheating inspection.