I turned on the heat for the first time yesterday morning to find nothing but WARM air at best. 80 degree air when the truck was fully warmed up. Assuming it was the thermostat stuck open, I replaced it last night when I got home, the antifreeze was horrible, mud red, probably original (155k miles). So i drained, but did not flush the antifreeze by popping off the lower hose at the radiator. With a new thermostat and antifreeze, I still have the same problem. I had the truck running/ drives around the block for approx an hour last night and I also noticed that there isnt any pressure built up when I take the cap off and after an hour of running, the upper rad hose is only warm to the touch at best. Since the only access to the coolant is through the overflow canister, is there a way to purge any air bubbles? This morning, I got a little pressure after driving about 15 minutes @approx 75 mph on the interstate when I stopped for gas but the warmest air I got was 82 degrees. I also noticed last night that when I squeezed the hoses, it sounded like breaking glass inside the hoses. Ok, I think thats all, tell me what I KNOW I dont want to hear...new radiator, hoses and heater core.

 

I would say start with replacing hoses it sounds like you have a blockage somewhere along the coolant system. I would pull the lower radiator hose and make sure it is free flowing. If all your hoses are free flowing odds are it is the heater core.

 

Does anyone know if there is a drain valve on the raidiator of a 2000 f150? I can't find one anywhere.

 

Looking into the engine, its on the bottom left of the rediator on 2000 5.4