By November 30, 2012 0 Comments Read More →

No Heat After New Heater Core Installed

leaking heater core
I had a new heater core put in my car and now I have no heat. I have bled the system, replaced the thermostat, replaced hoses, pressure forced water through the heater core, you name it I think I have done it.

I can get heat for a time but as soon as the car cools and is restarted the heat is gone.

The only thing I can think that is left is switching out the heater hoses thinking maybe the mechanic put them on the wrong side but this doesn’t seem to me that this would make a difference. do you have any other suggestions?



Hey there Peter,

Do the two heater hoses get HOT to the touch? If the heater hoses under the hood going to the core are hot (when engine reaches normal operating temperature) then you probably have a blend door or control head problem.

The blend door receives a signal from the control head that you have selected heat and closes off the duct from the A/C evaporator and opens the outlet from the heater core.

There could be a problem with the blend door motor, a restriction in the operation of the door or the door is not getting a signal from the control head to open the heater outlet inside the dash.

You could have a manual operating door that uses a cable or you could have a small blend door electric motor depending on what air conditioning options your vehicle has.

Since you mentioned that the heat changes once you turn the car off and restart the engine kinda leads me to believe you have an electric blend door motor that is restarting itself and partially opens the door when you re-cycle the ignition key.

If the two heater hoses are NOT hot…..then you are not circulating hot coolant around the engine. I would triple check to see if there is circulation in the radiator (both upper and lower radiator hoses should be hot to the touch), that the thermostat is working and that there is not an air pocket in the cooling system.

Here is a good video about By-Passing a heater core for those of you who want a cheap and easy temporary fix to a leaking heater core problem.

Posted in: A/C and Heater

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