Hey hows it going. I have a 2001 F150 with the 4.6L V8. The heater is not working correctly. After the truck warms up i turn the heater on and it gets warm for about 20 seconds then cools off. I have replaced the thermostat, flushed the radiator and heater core and its still not doing anything im at a loss and could really use some help. Anything would help. Thanks.

 

Sounds almost as if air is getting into the cooling system, possible leak or problem maintaining coolant pressure?

 

No the pressure is good I checked it yesterday. And I looked at the blend door motor today and it looked like it was working correctly.

 

See the other thread you posted in.