It could be a couple things. First, with the engine hot and the heat on, feel both heater core hoses. Both should be hot. If only one is hot, flush the heater core. If both are hot, check the blend door. Chances are it is stuck.
February, 9, 2015 AT 10:29 PM
Hi, I realize this is an old question, but I have a similar problem. What is the next step if both hoses for the heater core are cold? The hose from the radiator to the manifold is hot.