i have a 2000 f150 and recently the heat quit working ive checked the fluids there fine ive also checked the hvac temp control **** and that too is working properly...when i looked under the hood i noticed that only the top hose is gettin hot like it should but im not gettin any heat from the bottom one ive been told to change the heater core but im pretty sure that isnt the problem does any1 think that maybe the thermostat is maybe stuck open which isnt allowing all the hot water to flow thru the truck if not what should i do??

 

Heater core is actually what I was going to say.... Sounds like you've got it narrowed down to the 2 I would suggest checking first so....

I changed the heater core on my '93 fairly easy. Not sure how much more difficult it is on the 97-03 body style.

 

The heater cores in the 97-03 are a PITA you have to pull all the dash plastic apart in order to get to it. did it on a buddys expy it sucked

 

Disconnect both heater hoses and see if you can push water through the core with a hose. If you can't, it's plugged.

 

your heater core is plugged. do as glc says and take a water hose to it.

Alternate between the entrance and exit hoses to work the clog out.