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Q: Stuck thermostat?

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When driving the temp climbs between 210- 245. may bounce between the two temps. Doesn't drop when driving. Heater blows hot than cold. Heater has always blown hot.All these signs just started this morning. Is this a common sigh of a bad thermostat

My car has 218000 miles.
My car has an automatic transmission.

From what you described, it potentially might be a few different things that may be wrong with your cooling system. As you may know, when the coolant is pumped through the radiator to the engine, some of this coolant is recirculated back through the heater core. Heated air from this is blown through the vents into the interior of your car. The fluctuation in temperature may be also caused by a faulty or stuck thermostat which may cause the erratic changes in temperature. This may also be caused by a clogged heater core or even heater core hose leaks. I would recommend having an expert from YourMechanic come to your home to diagnose and repair your cooling system.

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