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Q: What would cause the temperature gauge to go cold to hot then back to cold

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When driving the car the temperature gage goes to normal temp then to cold then back to normal or hot an this continues happens when you are driving it

My car has 1300000 miles.
My car has an automatic transmission.

The engine temperature is regulated by the thermostat opening and closing to maintain the engine temperature. The cooling fan clutch also will maintain the engine temperature to keep a controlled air flow across the radiator to maintain the engine temperature. In order to test the system you will need to monitor the coolant temperature and the operation of the cooling fan clutch to see if the clutch is staying engaged too long causing the cooling system to get too low before the fan clutch disengages. Replace the cooling fan clutch if clutch operation is erratic. Replace the thermostat if the thermostat lets engine temperature get above 200 degrees F before it opens fully. The thermostat should maintain the engine temperature at about 180 degrees F.

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