Mr.T

The thought that comes to mind is mixing a radiator cleaner product and water to soak the heater core for a while, then flush for a long time in both directions.

Rednroll

I think I finally got this fixed!!! Third time is a charm....but I'm going to cross my fingers, but based upon on my previous experience and symptoms observed, this fix makes a lot of sense to me.

The root cause of the problem was that one of my front lower intake manifold bolts had broken, and I had never noticed it, because it was located below the throttle body assembly. This in-turn caused my lower intake manifold gasket to start leaking which allowed small amounts of coolant to leak, which let air into the cooling system.

So I just finished repairing my lower intake manifold gasket and replacing the broken bolt since last weekend coolant started to leak out of the driver side of the engine (the same side the broken bolt was on).

So here's my thoughts on all my symptoms and repair attempt observations.

Original Symptom: Notice cool air blowing out driver side vent on cold days, notice gurgling sound behind dash during start up on cold mornings.

Diagnosis: Gurgling sound behind dash indicates air in the heater core which is located behind the dash.

Repair 1 attempt: Top off coolant, burp coolant system to remove any air.
Observations: Heat worked good for about 30 minutes, then went back to blowing cooler air.

Hindsight 20/20 root cause: Small leak in cooling system in both the radiator and lower intake manifold, letting air into the system over time. When full pressure was present, right after fill/burping then heat would work normal but due to dual small leaks, which didn't start leaking until there was a high amount pressure and at higher operating temps within the cooling system, I was unable to observe the leaks while sitting still because they only tended to leak while driving which means the majority of the evidence was blowing away or was hidden out of sight (on top of front skid plate, along side of engine).

Repair 2 attempt:
Reverse/Forward flush Heater core, refill and burp cooling system.
Observations: Same as above, worked for a short period of time, I got excited, system leaked, air came into system, coolant level in HC dropped, heater went back to original poor working condition.

Repair 3/Diagnosis:
Considered I have a tiny leak in engine cooling system, purchased a coolant pressure tester to find leak. Observed leak in radiator end cap on driver's side only after bring pressure up to 18psi. Replace radiator, considered I didn't see any leaks because coolant wasn't leaking until pressure came up above 18psi to separate end caps from the core and the coolantd was additionally being captured by my AEV front skid plate. Pressure tested system after radiator replacement, didn't observe any additional leaks.

Observations: Heat worked well for 2 days and then started getting cooler again.

Hindsight 20/20 root cause: The lower intake manifold leak likely didn't show under pressure test because I tested it while the engine was cool. When the engine heated, parts expand and that's when the small leak likely started to occur, slowly while I was driving over a long period of time with the evidence blowing away in the wind. Since I repaired the radiator, the overall coolant system leaking was reduced, thus the reason the 1st 2 instances, hot air was present for 30 minutes, and after replacing the radiator it was present for 2 days, until it slowly leaked out of the lower intake manifold leak.

Repair 4/Diagnosis:

Observation: Coolant leaking from driver side of engine, top off coolant and a day later it was leaking from both sides of engine at a rapid pace.

Diagnosis: Leaking lower intake manifold gasket. While taking top part of engine apart to replace the LIM gasket, I noticed the front driver side LIM mounting bolt was snapped off. It looks like it had been that way for awhile but was hidden from obvious view.

Replace LIM Gasket, and replace bolt.

Heat is currently working great now!!! However, I also said the same thing after replacing the radiator, but that excitement only lasted for 2 days. Let's hope the fix stays this time.


Fingers crossed, but I think I finally got it fixed.

This was the root cause of the problem....missing bolt found missing during lower intake manifold disassembly.


Hidden broken bolt found after removing lower intake manifold (it's down there sitting next to that sensor electrical connector)


It's ironic because I mentioned the LIM gasket in post #42 as a possibility of causing my heater problems, but I eliminated that as being suspect since I never seen any coolant leaking in that area and it tested ok using the pressure tester, so I thought the LIM gasket was fine. The ghost just needed to give itself up by expanding that leak, so it became more obvious it was leaking.

Mr.T

I think you've got it whipped too, and it sure is nice to see the detailed follow up you did -- Others with similar symptoms will undoubtedly find it helpful.

Rednroll

Well, I'm back at it again. Cold weather hit, and while it feels warmer than what I remember from last year when it was cold, it's still not up to par.

I'm determined it's the Heater Core now.

The last time when I measured the driver side vent, it was around 80deg F. Now it's around 106F. So some improvement due to the radiator and lower intake manifold gasket repairs.

Here's what I'm seeing for vent temps.

HVAC Settings to take measurement.


Outside Temp 35deg F


Driver Side Vent 106.3 deg F


Center Vent 125.2 deg F


Passenger Side Vent 160deg F (What they all should be by the measurements Mr.T provided)

Rednroll

Before I did the lower intake manifold gasket repair, to avoid replacing the heater core I was working on a power flush system. I currently have that running. Here's what the setup looks like. If this works, I'll post a more detailed separate write-up. It is supposed to continuously circulate CLR through the heater core as well as heat up the CLR. Figuring hot circulating CLR will give me the best shot at clearing out any hard calcium deposits that might be limiting the flow of coolant through the Heater Core.



I purchased the following items

Fountain Pump from HF= $15.25 (w/ 20% off coupon)
https://www.harborfreight.com/264-gp...ump-63313.html


10 Amp 120V Thermal Temp outlet from Amazon=$18
https://www.amazon.com/gp/product/B0...?ie=UTF8&psc=1


1000 Watt 120V Hot water heater element from Amazon=$13.55
https://www.amazon.com/gp/product/B0...?ie=UTF8&psc=1

Rednroll

And this is what the setup looks like, currently working like a charm but questioning what's going to happen to that HF fountain pump with the CLR running through it and as the temp raises.





Heater Core Hose connections


Been running for a couple hours now.

CLR Temp now up to 68 deg C. The left number is the turn-on start temp CLR was originally at 7deg C. Middle number is the current temp of the CLR and the right number is the turn-off temp of the thermal switch. Gonna take it up to 80 deg C and let it run for awhile. I'm not sure what the boiling point temp is of CLR, but I'm gonna gradually increase it up to 95 deg C.

Rednroll

Well, my power flush setup worked really well.....it seems too well.

It was running for about 6 hours. My plan was to let it run over night. So I went to check on it, just before going to bed to make sure everything was still running good, where I noticed the level of the CLR in the bucket had dropped. I looked inside my JK and saw steamed windows and said "uh oh!!!"

So the setup worked so well, that the CLR must have ate through the heater core and sprung a leak inside. Previously, I had let the same CLR sit overnight in the heater core with no problems. So the added heat and circulation definitely did add some additional cleaning power. Hindsight 20/20, it looks like I should have pulled the plug on it after 3-4 hours. Lesson learned....replacement heater core ordered.

This is going to suck, replacing a HC when it's freezing cold outside but I was determined to not go another winter freezing inside of my Jeep. The power flush was my last ditch effort to avoid the HC replacement.

Mr.T

That's disappointing! Might be worth cutting the heater open after it's out for a look inside.

karls10jk

I've got to wonder if the heater core just isn't built for that kind of cleaning. I recall reading through the manual and coming across a piece that says something about not doing any sort of cleaning like that.

It is, however, informative to see what kind of heat the vents should be putting out . I'll have to check mine this weekend and see what happens. I've changed my coolant twice but never done any sort of flush.

Rednroll

I had originally thought CLR would be safe for aluminum, so figured I would be ok running hot CLR through the heater core, but I guess not. Previously, I filled the HC with CLR and let it sit overnight, but it didn't seem to do a good enough job to remove the deposits. The heated flush was a last ditch effort to avoid having going through the pains of replacing the heater core anyhow, so it was worth a shot. I'm going to do the cut away the dash cage HC replacement.
https://www.jk-forum.com/forums/stoc...0-mins-336039/


Hindsight 20/20, I think the heated flush likely worked because I noticed as I was going along the flow of the CLR stream had steadily increased from the hose that poured back into the bucket. I think the right combo would be to take the temp up to 80C (176F) and let it circulate 3-4 hours. I noticed once I started going above 80C, that the CLR started to foam up quite a bit. I took the temp up to 90C (194F).