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Q: No heat and the temperature gauge goes down.

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I changed the thermostat changed the heat sensor and changed water pump and the car still has no,heat unless it sits but as soon as you start driving the temperature Guage goes back down and car starts to get cold again please tell me what could this be

Hi there. Check the heater control valve on the heater hoses under the hood. The valve is controlled by vacuum. Check the vacuum lines and see if they have came off or split. With the engine at operating temperature, check the heater hoses before the valve and after the valve. The hoses should be the same temperature with the heater on. If the hoses after the valve are not as hot as the hoses before the valve, then the heater control valve is not working and needs replaced. If the valve is replaced and the heater still is cold, then check the thermostat switch for any loose contacts or damage. If you need further assistance with your heater being cold, then seek out a professional, such as one from Your Mechanic, to help you.

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