1999 F150 5.4L 4x4....replaced the heater core 11 months ago on my own to save the $800 quote I was given by a local shop (now I know why it is so expensive, literally removed the entire dash...fun, fun). Everything was working great. Now, no heat again and cold weather is just around the corner. Is 11 months all a heater core replacement will last? As far as I know, the one I removed was the original.

 

I have read other similar threads of members with heating problems. I will check all as I tear down the dash again this year.

 

Is it leaking or simply no heat??

How does your coolant look?? Dirty rusty coolant will plug up a heater core.
Air in the hoses will also cause it to not throw any heat.

 

Well if no leaks the only thing I can think is you still have air in the cooling system that is not allowing coolant too flow through the heater core and dispense hot air.

 

Check the "blend door" and the "blend door" motor,

 

hows the thermostat and hows ur water pump? my sis b.f. had similar prob on a jeep

 

Thermostat is new, first thing I replaced. Coolant is fine and not rusty or brown. I am curious about the air in the lines? Tell me more, how do I bleed the air. At least hopefully that is something I can do before tearing down the dash to look at blend door/motor.

 

I always do mine by simply unhooking both heater hoses, and using a garden hose to fill the lines and core up before plugging the hoses back in.

 

take your upper radiator hose off as you fill it... easiest way i`ve done it..

 

X2