lgrant

99 4.0 Classic 4WD Automatic

I think I know the answer but am posting thinking that some one might have a better plan. Since I've owned this Jeep (3+ years), it has never had acceptable cabin heat. The blend door seems to be working. I've got good A/C but, when looking for heat, only get a hint of heat when I rotate the temp dial all of the way to the right. Also, when moved all the way to the right, I can smell coolant for a minute or so and then the smell seems to goes away.

I'm thinking that the heater core is 1) totally gummed up and 2) leaking just a tiny bit. The right way to deal with this would be to replace the core but the job is a bear as far as I can determine. The weather is pretty good now so I have a window to correct the problem before the cold weather arrives. As an alternative to replacing the heater core, I could do the reverse flush and put in some stop leak. Has anyone ever had any luck repairing a heater core with stop leak? If so, what brand of stop leak? Would one of those liquid glass products work in this situation? I'm a little concerned that the reverse flush might open the flood gates.

doublechaz

I've never had any luck with stop leak, but I gave up on such things decades ago.

I have, however, run with the heater hoses looped for some time to avoid the leaking core. But of course that gives zero heat.

Sig220

I knew my 99 XJ had a heat problem...as in no heat. I put it off until this recent cold front and then got busy on it. I reverse flushed the heater core until the water was almost clean. Checked all my hoses while I was there and then when I could feel both heater hoses get hot after the engine was warmed up. I had suspected the blend door actuator motor, so I ordered one. When I had the new part in hand, I removed the old one (easy) and before removing the harness checked both the old (no movement) and the new (movement) and installed the new one. Instant heat! Out of curiosity, I took the old one apart and found that the electric motor was stuck. I freed it up gently with a pair of pliers and checked it and it too now works. Probably never will need another one!

Anyway, the OP posted that, "the blend door seems to be working". You need to confirm that it is working. Also, I don't put much faith in the leak stop idea. In my luck it will stop up what needs to be open and leave what needs plugged up open. Wish you the best. If your leak is not too bad, maybe get heat with a actuator replacement and wait and deal with the leak in the spring.

lgrant

I did the reverse flush yesterday afternoon (both directions) and didn't get much of anything coming out - water ran clear right away, just as soon as the coolant was evacuated. I took a gingerly approach and did not hit it with much pressure, afraid of further damage to a compromised heater core. My gut tells me that the water pump would not have any trouble pushing hot coolant through the core - no evidence of a restriction.

Also checked the to-from hoses with an infra red temp gun about 1' from the core inlet-outlet. At idle, T-stat housing was 193*; the top hose read ~185* and the bottom hose read ~130*. That seems like a lot of head dissapation at the core, which is pretty much the designed fuction of a heater core. Can anyone confirm that this is about right?

I'm going to get up close and personal with the blend door and related components today. While I have good A/C and weak heat, the speculation that "the blend door seems to be working properly" may be wrong and, when coming off of the cold setting and going to the hot setting, maybe it's only moving part way to the "good heat" position?

lgrant

I vetted the blend door yesterday and results were good. I posted the results in a separate thread. See https://www.cherokeeforum.com/f2/ble...alysis-259554/

Could someone that has good heat in a 97+ and an infrared temp gun check out the temp of their hoses about 1' from the heater core connections. Thanks in advance.

fb97xj1

If you can smell coolant inside the vehicle with the heat on, the heater core is leaking. A pinhole is all it takes to be able to smell it. The heat will carry the fumes thru the vents.

lgrant

Yes fb97xj1, I totally agree that the heater core is leaking.

lgrant

Today did the back-forward flush again and then did the vinegar soak.

This flush was with more pressure than the first one and it definetely blew out some crude.

Then, with hoses loose at the engine end, I slowly poured 1/2 gallon of white distilled 5% vinegar into the outlet hose. The resulting flow out the inlet hose was originally water but became vinegar fairly soon (after about a quart) and I continued pouring in (approx another quart) thinking the bottom half of the heater core would be water and that it would take time to mix and get the lower part mixed with the vinegar. I estimate that the resulting mix in the heater core was about a 50/50 mix of tap water and 5% distilled vinegar - it doesn't make any difference because I would of been happy with 100% vinegar. Once the vinegar was poured in, I let it set for 6 hours. Just before dark, I flushed it again, both directions, and when back to reverse flush the second time I let the clean tap water run through the heater core for about 10 minutes. During the initial reverse flush after the vinegar soak, there were a couple of moments where the water coming out the inlet hose stopped momentairly and then shot way out which is an indication that the procedure loosened some crude and that it was blown out.

Preliminary testing indicates much improved heat and no worsening of the minor leak. Give me a couple of days - expecting a cold wave over the weekend so should know something definitive by Monday morning.

lgrant

I did a 900 mile round trip to Eugene OR over the weekend. Freezing temps to and from. The heat worked wonderfully - close to assembly plant compentency. I'll live with the minor leak until the leak gets much worse (wet carpets) or until the A/C system involuntarily evacs the refrigants or otherwise fails. When any of that happens, I'll tear into the dash and replace core, etc.

Final thought: it's hard to tell if the great improvement in heat is mostly attributable to the "high pressure" back flushing or the vinegar soak. It's easy to do either or both so really no need to drill down to a precise answer.

Good luck to all.

318SixPack

Don't some Canadians just bungee in a propane heater on the passenger seat and run with that? Lots of survival skills to be learned from our friends in Saskatchewan.