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Why would the temperature gauge drop when the heater is truned on?


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Wiki User
2004-12-09 06:12:46
2004-12-09 06:12:46

The heater core is just like having another radiator, only smaller. Once you turn your heat on, and force air through the heater core with the blower motor, the engine's coolant's temperature is lowered, and circulated back to the engine, probably right where the temperature sensor is located.


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My Altima had that problem and it was the water pump going out. It started with temperature gauge was moving, but then it started leaking and finally the heater stopped being warm at idle.

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If you are absolutely sure you do not have air trapped in your cooling system then you may have a defective gauge if you are getting heat through your heater. Usually I would say you have a coolant flow problem with either a stuck thermostat or a bad water pump but if you have heat from your heater, then you must have circulating coolant in your system. I would check the gauge or the sensor.

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If the coolant level is okay, I would suspect a restricted heater core. Try flushing the heater core.

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The heater core may be plugged or not flowing properly. This would not allow the water to flow properly to cool the motor. Also you may have a bad or loose ground wire to your heater switch, this will give you a false reading on the temperature gauge.

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This would indicate that the system is low on coolant when the gauge is hot. Not enough coolant to service the heater core.

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