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

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Already replaced head gaskets, thermostat twice, and flushed coolant. It overheated in cool rainy weather, ac on auto temp at 77. Parked & checked. Main hose up front to radiator ? was hot and stiff but not scalding. Slightly hot smell. Plenty of coolant (the correct one for this model was put in during the flush). Drove back home with heat on and it didn't overheat again. Dash panel is starting to give (not coming on for first 5 minutes, gas gauge out, etc) but don't want to assume as the on board notifications say "engine coolant hot ".

My car has 170000 miles.
My car has an automatic transmission.

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.

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