Weird Heat Problem

I posted a message a month or so ago about the lack of heat coming out of the floor vents of my '87 4.0
I took everyone's advice, back flushed the heater core, replaced the thermostat, and still the air coming out of the floor vents is lukewarm at best.
The heat coming from the vents and defroster is nice and warm, but if I switch it to come out the floor, the air becomes lukewarm. Any ideas?

not to take over the thread but mine does the same thing. Id love to know why as well. also done everything you did to try and fix it. TWICE.

So when you switch it to floor vents does the air stop completely coming thru the deforoster vents and the dash vents ??

Yes, the air stops coming out of the vents and defroster.
I drove about 100 miles tonight in 30 (or so) degree weather. When I moved the lever to "Heat" the air only came out of the floor vents and it was cold. When I switched it back to "Vent" the air coming out of the vents was nice and hot (and air stopped coming out of the floor vents).

Thats strange, when the temp setting is all the way over to the right 'hot' and you move the other controller from defroster or dash vents to the floor mode all it does is operate a flapper inside the heater box.

Wife had something like that in her 87 (without A/C), 2-3 times. Once it was one of those push on nuts/retainers that fell off of a slider cable end, at a flap control arm, down by the heater box, passengers side. In defrost it didn´t seem to vent much heat (air) to the floor, guess the blower blew the heat control door shut, on heat the fresh air vent door would blow open and/or the heat door wouldn´t open and it would blow mostly cold air, mixed with a little heat. Got worse at higher speeds. Seemed to blow a mix of heat and fresh (mostly cold) air, even when the heater controls were off.
Second time it was the same cable, but on the heater controls.
Next time it was a disconnected vacuum line, that the body shop guys missed, when they replaced a fender. Don´t remember the exact symptoms, but think it was defrost/no floor heat or vice versa.
Next time it was the vacuum plug on the heater controls, that came loose.
Next time it was the intake, that was plugged with pine needles. Neither the heat or defrost worked well.
Seemed like most every winter, she would have to put on her snow suit to drive to work. :twak: In the summer it would heat just fine.

Mine does this and I've been told by folks here that it's a vacuum problem. One I've had no luck tracking down.

Sarge

I know this is an older post, but I've been out of town for the holidays and just saw it. It seems like this is a pretty common problem and I've had the exact same thing with my '88 and now my '90 so any suggestions would be greatly appreciated

hey i'm bringing this one back from the dead



i have this issue with my 90 exact same to a T heat blows warm through everywhere but the floor i haven't had much luck searching as you can tell be this thread i brought back but i would like to see if we came up with an answer, also besides this problem my heater blows very weak it work in all four fan settings but very weak until i put it on MAX a/c then it blows nice and heafty


forgot to mention my whole cooling system minus water pump and heater core is brand new


any help TIA

This is on behalf for my dad. He replaced the radiator a few years back (overheated) on his 87 XJ. He says ever since it was replaced his heater doesn't get warm. He recently put on a new 195 degree thermostat which didn't help. The engine doesn't seem to get as warm as it should either. I told him to check the thermostat again so I guess we'll see what happens.

My 88 XJ's heater never really worked that well. Seemed like the vent produced the most heat.