I have a 98 and a 99 cherokee both with the 4.0. Past 2 weeks have been bitter, with windchills in the 20's. The heat in both have been lukewarm at best.

Did some searching here, as well as you tube. I had done a flush as well as t-stat change on both - but it was still not warm enough.

There is a great video on You Tube by Eric the Car Guy - and he does a backflush of the heater core. Using an air compressor, and then CLR, then water - wait till you see the gunk that comes out.

Basically take the heater core hoses off and the inlet (off the t-stat housing) becomes the outlet. the other hose will become the inlet.

You place the outlet into a 1 gallon milk jug. And using an air chuck (wrap some electrical tape around it so it fits snug), insert the air chuck into the inlet hose (normally the outlet hose). This is what you will connect the air compressor to. I used 30 psi.

Blow out what's in it - more than likely brown sludge. MAKE SURE TO WEAR EYE PROTECTION. TO MUCH AIR AT ONCE WILL SPRAY IT EVERYWHERE. Also - wear latex gloves. (if you search for the video - it will show you step by step).

Next, I took CLR, and mixed with water (50/50 mix). I then poured it into the inlet hose (normally the outlet hose - of course you need to remove the air chuck to do this). You will be doing a little bit at a time - probably about 12 - 16 oz at a time. Let it sit - then replace the air chuck - blow out the solution. Repeat this till it is gone. Then flush with water several times.

It took a couple of hours - but now the heat is HOT! cost $6.99 for CLR at Walgreens, etc.

 

good to know, i'll have to try this out

 

Worked like a charm for me!

 

THANK YOU!!!

i am doing this tomorrow.

 

Awsome, I may have to try this

 

I have used this technique successfully. It is worth a try before tearing the Jeep half apart to put that new heater core in.....................

 

with the 50/50 clr mix, I flushed 4 times (56 oz altogether) then flushed with water 4 times (another 56 oz) I have a bucket of brown sludge. when you flush into the milk jug (acutally use a Chik Fil A ice tea gallon jug since they are crystal clear) you will see all the sediment settle at the bottom.

 

It fixed mine!!! Thankyou!!!

 

Trying this tomorrow! (fingers crossed)

 

I once had a heater core flush and yes it did resolve the issue....but the next winter the heater core began to leak, so I had to bypass it. Eventually I paid 350$ for a shop to replace it, could be even more expensive for an XJ??? I just got the feeling that if it's clogged, then it's not far from leaking... not sure though.... I did have some overheating issues with the vehicle that I guess could have possibly cracked the core, since it didn't have a valve system it was just hoses directly into the core....

 

yeah it worked wonders for me also did it today and WOW

 

I've had four radiators rust through since '98, and I'd been having a shop flush the heater core every fall for my '98 GC. So I gave it a try and it worked, thanks guys! The first shot of air was a bit too much. Blew the jug across the garage and spayed my beer fridge with gunk. My daughter is driving it for now so I feel much better during these cold months.