slapNtickle

Been having issues with my heater since I bought the truck used. 1987 f-150 5.0. The problem is the heater blows warm enough to keep the frost off the windows and thats it. The temperature gauge reads good and the fluid level is also good. I pulled the heater box apart to get a look at the heater core. Now my question is "Is the air suppose to flow through the heater core like a radiator?". If so that may be my problem. The air is blowing around it and not through it. The core is hot to the touch so I know the the fluid is getting in it.

NGM

Yes the air should blow thru the core like a radiator. Sounds like you may have a blend door problem if the whole core is 170 - 180 degrees.

slapNtickle

The blend door is just to the left of the heater core? I Messed with that while I had it apart and noticed that one way let colder air through if I turned the temperature setting colder. Maybe I should pull the core out and see what is going on behind it. The air is not going through it, just around it. Maybe something blocking it from the back side?

BIG D

You should definately make sure there is no blockage,then seal the heater core so that air cannot go around it. There is a foam that has adheisive backing on it,peel the backing off and apply it around the edge of the core so that when it is slid back in the case it seals against the foam. If the blend door is opening and closing fully and seating against the case seal,then your problem is most likely air flow thru the heater core itself. This should remedy your problem.