I have a 1998 F150 with 104,000 miles on it and have had some problems with the heating in the cab. The engine heats up and finally I'll get some warm air through the vents, then the warm air subsides and goes cold and the engine heats up again. I replaced the thermostat last night and the engine heat is now in normal range. However, the cab doesn't heat at all now. All I've got is cold air coming through the vents. What should I check next?

 

Hi and welcome to FTE

It sounds as if you may have an air pocket in the cooling system. Are both heater hoses hot?
You might try running it with the cap of for a bit to see if it burps any air out of it.
Jimmy

 

I'll have to check that out tonight. Thanks a lot, I appreciate it.

 

Blend door not opening, common problem on these trucks.

A vacuum leak allows the door to let cold in.

Sorry I can't explain better.