I have a 96 f150 4wd with the 5.8. I can only get Luke warm heat out of it. I have flushed the cooling system. Replaced thermostat that didn't help so I replace the water pump heater core and all the lines and another thermostat. On the first start up it had great heat took it down the road and it's the same ol crap Luke warm heat. Any ideas I'm tired of throwing money at it. And I checked the blend door it's fine. To the touch the hoses don't feel as warm as they should and temp gauge only runs at the n on normal. And you can watch it move up and down between n and o going down the road. Any ideas ?

 

Do you get less heat when accelerating or does it shift between floor and defrost? If so you have a broken vacuum line on the diverter door or inside the dash.

 

use a non contact temp gun and see what the hoses to and from the heater core are. also the temp of the upper rad hose.
they should all be around the same temp.
if so you will have to get into the heater box and find what is blocking the blend door from switching from AC to heat.

 

I know on some vehicles, if the fluid is low, the heater will not work well. Sounds like this may be the issue since you said it worked and then stopped after driving it. Once the thermo opened, the fluid became low and is not flowing well thru the heater coil. Just a thought

 

I did notice that when driving I can throw it in neutral rev it to 3000 rpm and it has heat. It is full of antifreeze and the over fill tank is where it should be. I can't find any vacuum leaks. Would it make a difference if the heater core line possibly got crossed? I'm sure they didn't and I don't think it should matter I'm tired of freezing my butt off driving it. I even have half of the radiator covered for the ride home from work and still no heat just luke warm

 

With the radiator half covered, and has been driven long enough to know it should be hot, check upper radiator hose. Is it hot? Is the hose tight? If neither of these are true, I would be inclined to suspect bad thermostat. What type of t-stat did you install? Stant or Motorcraft? Just a thought since I had 3 Stant thermostats fail within a year. TJC and Conanski noted good points considering blend door actuator and defrost control. Same goes for Afrans comment on fluid level, though you have confirmed fluid level.

 

we have a 96 superduty in work. the kid driving it used to freak out because it had no heat unless he was driving 55-60 mph.
everyone said the blend door was working, because the **** was turning.
i finally got a chance to get it into the garage.
i popped the heater core cover off, and stuck my hand into the heater box. grabbed the blend door and gave it a yank as i turned the ****. POP!!!
whatever fell down the defroster tunes dislodged, and the door moved again. i put it back together. the boss took the cable off the blend door to keep it on heat because it is a plow only truck.
the next time he took the truck out he called complaining the heat worked too good, he had to drive with the window down.

 

I second that, I had the same issue with the same truck, So we pulled the cover off the heater box and was able to reach in just enough with a smart phone with a flash and take some pics of the blend door although since you couldn't see it otherwise, a simple bic pen had fallen down the defroster vent and was lodging the blend door open although the cable still worked. A 10 cent item cost me hundreds of dollars and a cold truck in the dead of winter.

 

well here is a update i have taken all your advise guys and i still have no heat i dont know what is going on here everything looks as it should. this is so frustrating because i figure its something stupid that i cant put my finger on! If anyone has another suggestion on what to do i will really appreciate it. Everyone have a great day

 

I also have this issue with my 94 F150, 5.8L. I replaced water pump & thermostat last weekend, everything worked fine until Tuesday night on the way home, temp gauge didnt even get into the normal zone. Have covered half the radiator & still the same. Top radiator hose & both heater hoses are warm to touch, but not hot like they should be. Fluid is up to proper level and has not dropped. I am pestering friends today to try and find an answer to the issue. Will update if I find anything.

 

been messing around with the truck this morning everything seems to be heating up the hose going into the heater core from the top of the intake is real hot as should be but the return hose coming out of the heater core going back to the water pump is only luke warm not sure what that is. Im wondering if the system needs to burp. as i said before i just put a new water pump and heater core and another thermostat in this thing. i guess what is the best way to burp this thing? I normally just fill everything and let the truck run with the radiator cap off and have never had a problem before

 

My dad, who was a Ford mechanic when I was small, said to break the heater hose (the colder one) loose as close to engine as possible & check for flow & release any air trapped in core. NOTE: On my 94 5.8L, that hose connects to a pipe right over the Alternator, SO, I asked him if I could bleed it at the heater core, he yes - it would do the same thing. BTW - I did this same thing, but am looking to replace the thermostat again & re-bleed the system later today to see if I can get it to heat up to normal range. HOPE THIS HELPS.

 

if your heater core inlet is hot and the outlet is cold or just warm you have a blockage in the core or outlet line

hot in and warm or cold out means you are not getting anything or very little flowing through the core.

did you verify the heater core water shut off valve is open?

 

Has persons with luke warm heat/no heat backflushed the heater core? What brand of thermostat and temp rating has been installed? What radiator cap is installed? Motorcraft or sub par brand?

 

Stant 192 degree thermostat. (2nd one). Brand new heater core and water pump from ford dealer. On my 5.8