2001 F150 4.2 V6 heater not blowing hot air. does blow hot air for a few seconds, but then no more heat. turn off the heater and try again in a few minutes and again get a blast of hot air then it cools again. one of the hoses going to the heater core is significantly hotter than the other. backflushed the system and water is passing thru, but only about a 0.25" stream is coming out. am currently running flush thru the system. could it just be that the heater core is plugged...

 

Good chance. Have you ever run stop-leak or anything through your system?

 

never put anything other than coolant/water. im guessing my next step if the flush doesnt work is to pull the heater core and replace? at least it's back up in the 70's here this weekend...

 

Replace the heater core before you really need it

 

I just had this problem with my 98 F150......i replaced the water pump and i have heat...my heater core was not plugged or leaking......new thermostat, and blend door is good........try to find an old post from 2006 from a guy called NOHEATDAVE...it deffinitely helped me....good luck

 

If you only getting a fraction of what your putting into the heater core coming out it must be plugged. Is this something recent? Or have you noticed it gradually getting worse? if the heater core is severely clogged you might want to consider just replacing it.