Hello all
I hope someone can help me, I have a 94 F150, and I am getting very little heat out of the vents. The thermostat is new, the coolant level is fine, and the engine is not overheating, so I don't know what the problem is. Perhaps air in the cooling system? How do you purge the air out? Any help will be greatly appreciated.
Ray

 

If it's not running hot it's probably not air in the system--- but making sure there's no air is a good idea anyway.

Most likely causes are the blend door actuator or a plugged heater core. I don't know enough about the first, so I will speak of the second.

To check for a plugged heater core, disconnect the lines going to the heater core and run a garden hose through there. You can buy a nipple you can splice into the line or if you are cheap like me and don't mind a bit of a mess you can just hold the hose in place with your hand. The more plugged your heater core, the more resistance you will see for the water to come out the other side. Also probably the more stuff you will see flushed out. If it is not the heater core, you will definitely need to bleed it now, because you just put a bunch of air in it.

to bleed it is pretty easy: I normally start with the engine cold, remove the radiator cap, start the engine. turn your heater on high. As the engine heats up, the coolant will overflow a little. Once the upper radiator hose feels hot, this means the thermostat has opened. fill it the rest of the way with water/antifreeze, put the cap back on, fill the overflow to the proper level and you're done.

 

I finally got a chance to work on the heater in my truck, and thanks to Cliffordf150's good advice, I have heat again. The problem was a bunch of crap in the heater core, once it was flushed out it worked just like it used to.
So I just wanted to say thanks for the good advice.
Ray