Q: Heater system blows hot air when moving, but gets cold when car is stopped. Lower radiator hose is cold
My car was overheating and the radiator was leaking & the heater was blowing only cold air. I had the thermostat, radiator(and cap) and both hoses as well as the Coolant temp sensor replaced. The car is not overheating now but the lower radiator hose is cold and the heater only blows hot when the car is moving. As soon as the car comes to a stop, the heater begins to blow cold air again.. What could cause these symptoms? Faulty thermostat, water pump, coolant blockage?
My car has 108100 miles.
My car has an automatic transmission.
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The lower radiator hose should be much cooler than the top hose. As engine speed increases, so too does the flow of coolant through the heater core in the passenger compartment. If the heater control valve (operated by the temperature control on the dash) is not openly completely and/or the heater core has scale or obstructions, that would explain why heat is not adequate until the flow rate increases. At idle, the flow rate will be sufficient as long as there is no obstruction to, or through, the heater core. The foregoing is just one possible cause of the low heat at idle problem. If you want the cause pinpointed, please request a cabin heater diagnostic and the responding mechanic will get this resolved for you. If you have further questions or concerns, do not hesitate to re-contact YourMechanic.
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