Heat issues

Cotterpin

Cotterpin

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Joined
Dec 11, 2019
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45
Location
Eastern PA
As stated I’m having heat issues with my 03 TJ. At first it wasn’t throwing any hot air so I flushed the system and had gotten a lot of sludge out of it, (I believe my Jeep sat for a while before I bought it), until the water ran perfectly clear. Still no heat though so I flushed it again with more cleaner. Heat was 150 at the vents but when I set it on the defrost/floor setting it blew hot out the defrost and Luke warm out the drivers side and cool out the passenger side. I thought it might be in the blend door but all the controls seem to work. I back flushed the heater core, cleared it, filled it with white vinegar and let it soak for about 2 1/2 hours. Flushed it out refilled it with antifreeze hooked it all back up topped off the radiator left it run with heat in high kept an eye on radiator level. It was better but the passenger side still wasn’t as hot as the driver side. And then after about 25 minutes of driving it seemed to be back to Luke warm drivers side and cool on passenger side on defrost/floor setting. I’m going to try it like this for a while and flush it again.
Any suggestions or ideas?
Thanks.
 
Do both of the heater hoses at the firewall fell about the same temperature to the touch while hot?
 
Flushing out the heater core needs to be done with the two hoses switched positions. Otherwise you are pushing junk into the core. The bigger gunk stays. By switching the hoses around you are flushing the core from the opposite direction. This forces the goop back out the way it came. The bigger crap can now come out. And then you can put the hoses back to normal (or leave them backwards. It does matter to the heater) for the refill.
 
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If your heat was 150 at the vents and/or the defrost, your core is doing it's job.

Only luke warm out the drivers side and cool out the passenger side, while the other was hot, it's probably something with the door, the controls or what is between them.
 
DirtyD. Yes both hoses are equally hot.
Goatman. I flushed the heater core in reverse direction both times. The first I got a decent amount of dirty water but the last time it was very little even after the vinegar soaking. I’ll try reversing the hoses and running it that way.
JeepCJTJ. That’s what I was thinking but all the controls seem to work. I even took off the motor on the blend door and worked the door by hand. You can definitely hear it move and Hit the opposite side of the box. Unless it’s a series of doors that have to move inside the box. I’ll check it again.
 
When I was replacing the front speakers over the summer I somehow bumped the heat tube going to the left side dash vent and it popped off the vent completely. Had to pull the gauges and some other parts to give me room to reconnect the vent. Is it possible you have a similar problem? I know both my side vents flow considerably less air than the center vents. I doubt there is much that can change that. The length of ducting just slows the air down I think.
 
Goatman. I’ll check that out. I took a look to swap the hoses at the heater core and remembered they are two different sizes.
If nothing else works I’ll try another flush.
 
So I had a similar issue on my 2000 TJ (4.0L).

Situation:

I recently bought the Jeep used (three other owners besides me) and it has roughly 92K on it. The heat was not working (blowing luke warm at best). The coolant was brown (rusty), so the last owner and used car dealership clearly didn't take care of it.

Actions:

I flushed out the system twice and then targeted the heater core alone and reverse flushed that as well. I got a lot of build-up out of it doing that. Afterwards, I filled it up w/ distilled water & Prestone Radiator Flush + Cleaner following the instructions and ran the vehicle for 3 days under normal use.

The interesting part was that the heater worked perfectly over those three days; average read out from all vents was around 130-140.

Issue:

The issue for me now is that when I filled it up with coolant I'm only getting 95-105 degrees of heat at best. The lower heater core hose is not nearly as hot as the top hose. I know the thermostat is working since when I filled up the coolant and let the car idle to temp (w/ the rad cap off) I heard a click when it reached running temp and saw the coolant level in the rad drop as the thermostat opened and filled the engine. I then topped off the coolant. I also did the following things:
  1. Made sure to burp the system (leave the rad cap off and pump the top rad hose until it stopped bubbling),
  2. checked the coolant levels in the reservoir,
  3. made sure the vehicle was not overheating while in use,
  4. and made sure I didn't have any leaks (left cardboard underneath the vehicle to see if there were any leaks etc., after running it).
Question:

Anyone, have any ideas as to why it will reach perfect heat temp w/ distilled water and flush cleaner but not coolant?

Notes:

I replaced the following parts over this process (see below). I didn't replace the rad cap since it looked ok but I'm considering that as well.

Replacements:
  1. thermostat,
  2. thermostat sensor,
  3. water-pump & fan clutch,
  4. serpentine built,
  5. rad, and,
  6. all heater hoses.
 
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If your heater hoses are running different temps it's a sure sign more crap found it's way to the heater core. You'll need to flush the whole system out some more. It seems some heaters are a lot more likely to plug up than others. I had a neighbor thy had literally chunks of rust swirling inside his radiator full of chocolate milk (70's Chevy pickup) and never had any cooling system problems.
My guess is Jeep uses a heater core with much smaller internal passages. Flush some more. If you can save the coolant and filter it well you may be able to reuse it. But don't put it back into your Jeep. An old JD tractor or something you only run in the summer (old) could be ok.
 
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Goatman,

Thanks for the quick reply!

I suspect your right and will flush out the system again and through in new coolant. TJ heater cores due seem really temperamental. With the cold though this is nothing something I want to push off, so looks like I have a weekend task to knock out!
 
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I cleaned and flushed out my heater core again this past weekend and still only blows Luke warm on passenger side feet.hot everywhere else though.
 
That is strange because on my '04, the lower vent is a single piece (just did my heater core). Could there be a blockage inside of it? It can be removed with 3 screws.
 
You said lukewarm on the passenger side foot vent. Is it warmer on the driver side foot vent? If so, there's probably a blockage in the lower vent because it's all one, hollow piece.
 
Ok. I’ll look for a blockage and let you know if I find one. But it seems to push as much air as the driver side. That’s what puzzles me. I wish I had a diagram of the vent system so I can see what to look for without tearing the dash apart.
 
The Jeep heater core has been a weak point in the vehicle since they first added a heater back in the early days of the CJ. Yet the FSJ I've never heard of a problem.
 
Cotterpin said:
Ok. I’ll look for a blockage and let you know if I find one. But it seems to push as much air as the driver side. That’s what puzzles me. I wish I had a diagram of the vent system so I can see what to look for without tearing the dash apart.
Click to expand...
Have you downloaded the FSM yet? You can find it here for your model year. The section you're looking for is 24-32. I just had my 2004 apart to do my heater core, so just ask if any of it is confusing.
 
Goatman said:
The Jeep heater core has been a weak point in the vehicle since they first added a heater back in the early days of the CJ. Yet the FSJ I've never heard of a problem.
Click to expand...
I don’t think it’s a heater core issue. I’ve cleaned and flushed it 4 times now. Both hoses are equally very hot and it throws excellent heat when set on defrost and on center vent. But when on defrost/floor and just floor it blows luke warm out passenger side.
The hot/cold blend door “seems” to be working as well.
 
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Cotterpin said:
Ok. I’ll look for a blockage and let you know if I find one. But it seems to push as much air as the driver side. That’s what puzzles me. I wish I had a diagram of the vent system so I can see what to look for without tearing the dash apart.
Click to expand...
BleepinJeep has a video on their website called "What's Inside a Heater Core Box." that shows how all the damper doors work. It might be helpful if you want to see how the box works on the inside.
 
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