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Q: Heater gets hot but then blows cold when idling or driving.

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heat gets hot then cold when idle or driving i have changed thermastate and new coolant

My car has 45000 miles.
My car has an automatic transmission.

This may be due to a faulty heater blower motor or potentially a bad heater core. As you may know, the heater core is a small radiator like unit that circulates the hot coolant from the engine through the heater core which then uses this warm coolant to heat the inside of the car with the help of the blower motor that blows the warm air through the vents inside the car. To avoid any unnecessary repairs, I would still recommend having a certified expert, like one from YourMechanic, come to your location to diagnose your heater issue firsthand and make the right repair.

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