Okay guys I’ve had the Jeep about a year now and the heat has never been the best. When I first got it I did a coolant flush and and back flush on the heater core with a new thermostat as well and the heat got a little better. So now year later I back flushed it again with good connections till the water come out clean. The heat is little better but when you turn the fan up higher the air gets cooler and on different settings also!!! I replaced the heater core lines also and there scolding hot going to the core. I can hear the door open and close and it’s cable actuated. The cable is on there and looks good and not broke!!! This is gonna be my sons Jeep and we need heat for winter coming up in Tennessee. ANY HELP WOULD BE GREATLY APPRECIATED!!! I’m bout ready to blow it up😆!!

 

Bad news. Sounds like the heater core is plugged up/scaled up. If it's hot at low speed, then it is transferring enough heat to the fins (fins like on your radiator - heater core is just a small radiator) to support low heat. But once you turn up the fan speed, then the heater core can not transfer heat to the fins fast enough. Only so many options there - coolant flow rate or heat transfer rate in the heater core. Pull the outlet hose to the heater core off and see if you get good flow out of the heater core.

You can still have crud in the heater core and have good flow through it. Have you done a chemical flush? BlueDevil Radiator Flush is a good one. Be warned - it may find a hole in the heater core, but what other choices do you have? Next solution is replacing the heater core. You likely have to pull the dash out - I haven't had to do one on a XJ. If the flush doesn't get it, then replacement is about your last option.

One more thought occurred to me - perhaps there is a bunch of leaves or something blocking air flow across the heater core? If your heat transfer is only taking place on a small portion of the core due to foreign material blocking the air flow then effectively your heater core is much smaller.

 

Also, make sure that the hoses, thermostat housing and particularly that steel line down to the water pump aren't clogged up either...

You didn't really say how you flushed the heater core, and maybe you did it this way, maybe not, but what I do is use a 5 gallon bucket and a pond pump. Pump to heater core and then back to the 5 gallon bucket. Add some radiator flush or white vinegar to the water and let the pump do the work. With enough time, barring finding a leak, it'll be good as new...

 

If BOTH heater hoses are hot near the firewall, the core isn't the issue.

 

The first time I back flushed I just used the prestone stuff from the parts store. I let it sit for bout an hour in the drive with the heater on high and then flushed after. The second time I didn’t use anything just back flushed it water and it seemed to running clean! I’ll try the blue devil and see what happens. If it had leaves or something blocking the coils how in the heck would I begin to get em out with it being so tight in there and both hoses at the firewall are very hot!!!

 

If both heater core hoses are hot and stay hot, he heater core is not clogged. Coolant is flowing through it fine and that is not the problem. But it could be partially clogged as said above.

warm the engine up. Once it is hot, turn the heater all the way hot and the blower on high. Check that both heater core hoses stay hot to the touch. If the exit hose is cooling down drastically then the heater core is probably to blame. You can flush it all you want but if it is bad enough you will never fix it.

You can also have someone inside the vehicle to tell you if the air coming out is getting cooler or staying hot. An infrared thermometer would definitely help with this job you can check each radiator hose and tell if one is cooling down.

 

The bottom hose is not as hot as I thought it was going into the core and I noticed the ac clutch is engaging on and off when the heater is on full blast is that normal??

 

It depends. What setting do you have the control **** on?

Any of the blue ones and defog will be AC on.

But even with the AC running, you should still have full heat. You have a blend door issue.

 

I've got it on the other selections, isn't the blend door cable actuated? If so mine is good the cable isn't broke and I can hear it close and open!! The heat has got better from yesterday it seems like every time I flush it the heat gets hotter!!!

 

It may not be moving into position the entire way. I had a problem with an old Civic where the cable was stretched or the lever was bent and the door didnt go the entire way. I had to reach down and move it the last half inch or so.

Im not sure what exactly it looks like inside but the door could have a foam or rubber seal that is gone or deteriorated. I've had that problem in the past with a different vehicle

 

Is 98 cable operated blend door?

 

I think it uses a motor that moves the door from hot to cold .You can look it up on Rock auto to see what it looks like .then find it to if it is working .

 

I think so too. The body change in 1997 included this "upgrade", Don't the gears strip or something?

 

This 98 has got the cable and everything seems fine!!!

 

Have you checked the adjustment and travel?
Disconnected the cable and moved the lever to verify it goes in both directions completely?