I have a 97 F150 with 150,000 miles. I had antifreeze smell in the cab back in the summer so I used stop leak. The problem went away and never had any problem with the AC. My heat has not worked since I first tried to use it this past fall. Neither heater hose is getting hot. The top radiator hose doesn't always contain any solution (I can compress it with my hand), but the overflow tank is full. I took the heater hoses loose and forced water thru the heater core in both directions (no problems). I then forced water thru the unconnected hoses back the opposite direction and it flowed fine (both directions). I changed the thermostat (even tested it without a thermostat), I changed the pressure cap and no difference. The engine temperature comes up to normal from overnight quicker than I'm used to ( about 1 mile in 35 degree weather) but seems normal and the engine has never overheated. I don't believe my problem is under the dash since the heater core is not stopped up and the blend door changes air speed switching from cold to hot, anyway the heater hoses never get hot going into the heater core. Does anyone have any suggestions? I appreciate any suggestions.
My next step is to take it to Ford and take out a loan.
Thanks,
Dan Benson

 

I have read your problem and it sounds like I am going to have to also go to the ford house. I am having the same problem with my 97 ford f-150 when i kill the engine I can hear the leak but i cannot seem to find where it is comming from. any help would be great.
thanks
mike

 

When you replaced the thermostat, did you ensure that you put it in correctly? Pellet end down.

 

Yes Sir, the thermostat is installed correctly. Do you know where the heater core is fed from? There isn't a lot of room under the hood but from what I gather there isn't a feed from the water pump as in most older engines. I thinking this is where my problem lies. I can trace the heater hose connecting to a hard pipe going back behind the engine but I can't determine where it goes. The other side of the heater core connects to the intake at the back of the engine.

Thanks,
Dan

 

On the 4.6L and 5.4L motors, the heater hose connects to back of the water pump, under the intake manifold.

 

On the 4.2L V6 the heater hoses go over the top of the engine.

Regardless of engine, find the heater hoses and see if they get hot before the upper radiator hose. If so, the thermostat is probably ok.