I have had off and on (mostly off...) heat for, well.. since if owned the jeep. I have flushed the whole coolant system, and I flushed the heater core with CLR and it flowed right through, there was no clogs or anything.
So, I put it back together, put a new radiator in it, and a new thermostat (that seems to be working, stays right at 210. Old working thermostat sat it right at 180).
So after all that, I parked it up on ramps in the driveway, pulled the rad. cap off and let it run for probably 20-30 minutes until all the air bubbles came out. The heat worked pretty good for about a day, then went back to just air..
The next week, did the same thing, thinking maybe more air bubbles were trapped inside the coolant system. I burped it for another 30 minutes and then re-filled with coolant as needed. The heat worked for about 2 days, then died off. It is luke warm at best now.

I dont have a cap for the overflow bottle, so for now I have been covering it with tape (redneck, I know).

The top heater core line is pretty hot, the one below it (retrun line) is not as warm, but nonetheless pretty warm.

I noticed that its harder to turn it from hot to cold, than it is to turn it to from cold to hot. Hot to cold I feel like the **** has some kind of air pressure resistance (vaccum?). When I turn it to hot from cold, I dont get that "compression" feeling. Could this be something to look in to?

I live in maine and the winters here are cold. Is there anywhere else I should look before changing out the heater core?
Thanks for any help!!

 

do you have a control valve in the heater line if not search heater blend doors

 

Heater coolant flow control valve? (Under the hood)

 

No.. post 96 (I think?) dont have that valve... or at least mine doesnt. both lines just go straight to the heater core

 

There shouldn't be more than 10 degree difference between your incoming and outgoing heater core lines. Sounds like you got a plugged core. Did you reverse flush the core?

 

Or could it be your waterpump?I had to replace mine this week and now the heat is good.

 

could have a busted vacume can thingy, does your cruise control work? I think they both run off the same thing

 

If you are at 210 for coolant temp, the engine is doing its thing.

The problem is most likely a HVAC blend door issue, or sorry to say it but that heater core is still in play. Sometimes flushing doesn't do the trick.

 

I flushed it both ways for probably 30 minutes going back and forth. I can blow through the lines and the air goes right through..water flows right through

 

So, is your XJ a '96 or post '96 (which is '97 and later).

 

I'm having the same problem with my 99' except mine doesn't reach 210 anymore, it stays just below. I've flushed the core, replaced t-stat (195), bled system, checked water pump....I've been posting in all the threads I can find on this subject hoping to get as much input as I can, it's cold!!

 

For leaks??????? Not sure what u mean? The service manual does say the water pump could be suspect in cases of no/low heater performance. How old is it? Someone posted that the heater trap door was cable operated....could it have broken/slipped off?

 

going to check the blend door and cable... ill post up when im done and see what I find out

 

It's probably your heater core. If your heat is a little warm/practically cold it's definitely your heater core. I just had mine replaced and now my heat is nice and hot. The only issue I have now is my **** for my hot/cold air won't move and I need to find out how to fix it (I was told to somehow stick my hand into the center console/dash and move my blend door for a temporary fix but I cant figure out how to). Replacing your heater core isn't a big deal if you know how to do it, we were told it would cost 1500 to fix it, but instead we had my uncle do it and it only cost 100 for the core (which for some reason didn't fit properly and had to be wedged into the plastic) and we gave him 150 for labor.

 

I'm having the same "little warm/practically cold" heat problem also and I'm pondering on replacing the heater core but before I do I'm curious to know what exactly defines a "bad" heater core, what's not working about it??