Can heater question.

I've got an '05 F250. While driving down the road the heater blows hot air. While idling the heater blows cooler air. I'm thinking it's a partially plugged heater core. Anyone else got an idea? The engine coolant temp stays steady dead center of the temp gauge. The engine warms up normally then stays warm the entire time the engine is running. No coolant leaks anywhere. Thank you for your input.

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Headgaskets. How's cooling system pressure? I bet upper hose is hard as a rock.

Could be a water pump coming apart as well, typically those will overheat though. Other than that I second the head gasket diagnosis...


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How about the blend door, maybe?

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Blend door wouldn’t change with engine speed


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You need to get a scan tool that reads the engine parameter data to get an actual coolant temperature. The dash gauge is useless.

Several good phone apps - ForScan and Torque Pro

You should also consider installing a pressure gauge on the coolant system. You can "tee in" a gauge on one of the small vent lines going to the degas bottle.