Heater warm at times, but 20+ minutes later turns cold. 2013 Town and Country

country7

I didn't believe my wife, but the heater starts blowing cool air after a period of time. I drove the van twice this weekend and both times the initial heat temperature did seem a bit cooler, but not problematic. After driving a for a while (20 plus minutes) the heat turned cool and remained that way for the final 10 minutes. The first time we where on the highway, but the second was in town. Engine temperature ranges for 178 to 230 and problem does appear to happen once temperature is goes above 220. Coolant level is between min and max. Problem may occur after switching to defrost though switching to defrost doesn't make it happen every time.

Mr_Shiftright

It would be interesting to test this--when the temp goes cool, to jump out of the car (after parking it of course ) and feel the inlet and outlet hoses in the engine compartment, that go into and come out of the heater. If the inlet is hot but the outlet cold, then you have a heater core or heater valve issue, which might be a clog or some electronic issue with the HVAC system. If both inlet and outlet are cool, then I'd suspect a bad thermostat or even perhaps a slipping impeller in the water pump. I doubt if both inlet and outlet could be really hot to the touch if there's cool air blowing into the car.