When I try to run the heater my thermostat gets stuck on ...

Q: When I try to run the heater my thermostat gets stuck on C and my car reacts like it is overheating.Sometimes draining the coolant

asked by on November 13, 2017

When I turn on the heat or defrost on my dashboard thermometer gets stuck at the bottom on C. Then the sensors start lighting up telling me my car is overheating. When I check the coolant levels (after the car has been parked for awhile) sometimes it is completely drained, but most of the time there is still coolant in the radiator and the reservoir. This sometimes lasts for several days and then goes back to normal (as long as I don’t turn on the heat) but this time it seems to be stuck.

My car has 200000 miles.
My car has an automatic transmission.

You may have a clogged heater core that may be prohibiting the outer linings of the heater core to get hot. As you know, the heater core is a series of tubes that the coolant runs through that generates the heat from the warm coolant after circulating through the motor. These tubes can occasionally develop a buildup on the inner walls such that when the heater core is "flushed" this buildup on the inner walls of the lines remains and still allows the coolant to flow through the heater core. It is important to note that when the heater core is "flushed" it is possible to get good flow through the heater core while the inside walls of the heater core remain caked with buildup. As a result, the buildup on the inner walls prevents the temperature from rising to its capability due to the insulating effect of this buildup on the inner walls which will prevent the necessary heat transfer to properly heat the inside of the car. I would recommend having an expert from YourMechanic come to your location to diagnose and replace your heater core.

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