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Q: Temperature in car stays cold

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I have had my car overheat and then at times not show it's hot at all. I have changed the thermostat 3 times in the past 2 years and feel it's something more. Heater has a wired smell and leaves fog on the windows

My car has 85600 miles.
My car has an automatic transmission.

A: Hi, thanks for writing in. The heater smell...

Hi, thanks for writing in. The heater smell and condensation/fog you see on the inside windshield are the results of a leak in the heater core. Coolant from the engine circulates through this "mini-radiator" under your dash, providing heat in the passenger compartment. You are correct in replacing the thermostat to ensure the engine heats up to design temperature quickly. However, the coolant leak is likely coming into play, creating air pockets in the engine that both allow overheating, and can register as "cold" on your temperature gauge. The temperature gauge sensor requires coolant on the sensor to register correctly. Air pockets don't transmit heat to the sensor, so it reports a lower temperature than exists. Replace your heater core, and eliminate any other leaks which may exist. Refill with coolant, bleed the cooling system thoroughly of all air pockets so you are getting accurate temperature readings and maximum cooling from the cooling system. If you would like help, consider having an expert automotive technician from YourMechanic come to your home or office to inspect and diagnose this issue for you, and make or suggest any repairs as needed.

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