I am new to this site, but I have found a lot of good advice here, so I thought maybe someone could help me with this.
I have a '93 F150 with the 4.9L I-6. I recently changed the water pump (leaking) and changed the thermostat, hoses, and radiator cap. I also flushed the system. After all of this, I am not getting anything above lukewarm air out of the heater. I also have somewhat erratic temperature readings. Here's what I've done so far:

- Bled cooling system of air
- Verified (and replaced again) thermostat (192 deg)
- New radiator cap (13lbs)
- Flushed and bled again (including heater core)
- Verified operation of damper door for hot/cool settings

A little more information:
- It doesn't overheat (gauge ranges from just below N to O)
- Both heater hoses get hot
- Upper radiator hose gets hot after Tstat opens

What should I try next? I am wondering if I need to try another water pump. I am also considering reversing the hoses to the heater core (maybe I didn't put them on correctly when I changed the water pump). I don't think this should matter since the heater core should just be a pass-through device.

Thanks in advance.

 

Is it possible that a fresh air vent is stuck open and mixing outside air with heated air. I had this happen once on a previous car, not a ford.

Sounds like the heater is getting nice and warm since both heater hoses are warm. Unless the heater core is partially plugged. I would think the return heater hose would be noticeably cooler. If it seems the same temp are the input heater hose then I'd say the heater core is not taking away much heat.

 

Hello! I had problems with my 92 F-150, about the same thing, replaced thremostats, waterpumps, and anything else I could think of, even flushed the heater core, but same thing, no hot air. Finally, I just decided to change out the heater core, and sure enough, hot air finally poured out. About everyone I talked to, including FOrd dealerships, said those heater cores go out often, so you might want to try that. They ain't that expensive, just time consuming to change out, but, its better than freezing! Just thought you might want to consider that as a possibility. Good luck!!

 

92 150 4x4 S40d My bet is on the heater core, had my system flushed and that didn't fix the problem.
The 2nd time time just the heater core was flushed hard. Ever since then i get a lot of heat and i did all the things you did before hand. GOOOOD LUCK

 

I did a heater on a '88 f-250, they are relatively quick and easy to replace. Took at most a 20 minutes. It cost 20 bucks from napa and they had one in stock.
1) Remove the hoses to the heater core after draining enough coolant.
2)pop out the glove box
3)remove seven screws holding the plenum cover on
4)pop the cover off and pull the heater core out.
Installation is reverse of removal.
With this kind of turn around I see no reason not to replace it

 

I'll give it a try. Thanks for the help. I'll let you know how it turns out.

 

Finally got a chance to replace the heater core. I have plenty of heat now. Thanks for the advice!

 

I have the same issue. I have a 94 F150, the heater core was replaced, new water pump, new thermostat. The system was flushed. Had heat at an idle but anything above an idle, the heat went away. Come to find out, the bypass and return line from heater core were reversed. Now have heat at idle and when driving for a bit, then heat cools off some. The door behind the heater blower fan operates as it should. Any other ideas to try? Temp on the temp gauge reads anywhere from the "N" to between the "O" and the "R". I am really baffled now. I am keeping an eye on the coolant level, making sure the coolant is good in the overflow tank. Any thoughts or ideas would be great.