Why No HEAT??
I have a 99 F250SD with a 5.4L, base package w/o AC, standard cab. I cant figure out why my heater doesnt work full time. I purchased this truck with the heater not working at all really, but I was thinking no big deal...easy fix. I guess I was wrong. So far I have flushed coolant through all the lines about 3 times since I switched out the heater core and replaced the intake manifold, so I know the heater core is working and good. I checked the blend door and that is working properly. If I start the truck up and let it idle it will heat up to about 65 degrees when it is around 35 degrees. If its colder out then it will heat up slightly less at idle and parked. The problem is once I start driving down the road, cool air starts coming out of the vents, enough that the truck slowly starts to get cold. I have tried cardboard in front of the radiator and it doesnt matter, which it shouldnt because my temp gauge is reading where it should be at all times. The heater core will burn the shit out of your hand when its parked and at idle but then cools off quickly driving down the road. Just dont understand how the heater core would cool off driving down the road? Its not like air cold air is blowing on it, its inside a box. Anybody have any ideas what would be wrong? Thanks