confirm diagnosis for me

[beerhiker]

I have a friend with a 99 TJ and the heater is going out. Heater blows luke warm at idle then warms up when driving then back to cool at stop lights, sometimes doesnt warm up at all. So I assume its the heater core that needs replaced, correct?
And I assume the core is way up behind the dash and is a pita to get too?

Thanks

 

[2drx4]

Has he got a water temp gauge?

I would think the thermostat is stuck open. Cores either plug, or leak. If it plugs, you will get no heat... If it leaks, the coolant on the floor will tip you off.

 

[beerhiker]

thats the 1st thing I checked also.....her temp guage is showing normal.
No leaks on floor. Thinking partially plugged, that would explain heat/no heat?

 

[beerhiker]

I think I better double check her temp guage to see if its really getting up to 200. That would make more sense to have a partially stuck open thermostat, since its goes warm/cold depending on idle speed.

 

[sandalscout]

Yep, sounds like the same thing to me, I believe my thermostat is stuck open on my jeep (no temp gauge, yet) but after playing around with it, I'm sure I'm getting flow to the heater core, just not much heat. I can drive it for an hour or more, and with it still running, I can grab the upper hoses and they are warm, but not hot.

 

[jeepmedic46]

How is the radiator fluid? My Liberty was doing the same and turned out to be my fluid was low.:REOutIceFishing:

 

[beerhiker]

Ill go tell her to check the level, see what it looks like, thatd be nice easy fix.

 

[jsolorza]

also check the coolant bypass valve to see if it opens properly.

 

[sandalscout]

Oh yes, good point, I didn't realize that they had those in the 99s still.

 

[IH8RDS]

I have been battling this with my XJ for over a year now. I think I finally got it licked.

Things I did:

Flushed entire cooling system. (temporary improvement)

Reversed flushed the heater core. (Worked temporarily but always came back after a couple of days)

Changed thermostat and flushed system. (a little better, but not up to par)

Took out and cleaned the entire cooling system and changed water pump. (After all that it still wouldn't work.)

I finally manually filled the heater core (from the larger line) with water and hooked it up and it worked.

I feel that it was an "air trapped in the heater core" issue. But I am not for sure. It would always work temporarily after flushing out the heater core, and sometimes I would actually get small particles to come out. It was never really enough to clog up the system though.

Maybe after completely removing all on the cooling components, cleaning and reassembling it fixed a small leak that was letting air in. Who knows. It has been working strong for a month now. I did notice when changing the water pump there was traces of it leaking around the mounting surface.

 

[I Leak Oil]

Yes, the symptoms make it sound like a coolant level, or most likely air trapped in the system issue.
Jason T.

 

[BigAl]

It sounds like a bad core to me. The job is not hard, just very tedious. You need to drop the steering column and remove the entire dash. It took me ~6 hours on 97. There are step by step instructions floating around the web somewhere. Good luck