Very little heat- Diagnosing the source of the problem?

Discussion in 'KJ General Discussion' started by WheelNut, Feb 22, 2021 at 2:15 AM.

  1. WheelNut

    WheelNut New Member

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    Hi guys,

    First post here! I recently bought a $1000 KJ as my first 4x4 and she's a bit rough around the edges! I was looking for a nice XJ, but of course finding a 2-door manual that isn't wrecked is impossible and the KJ was definitely in my budget. Also, who doesn't like a project?! Oh, and I can scratch up the KJ in the bush without any worries.

    The problem:
    Very weak heat from the HVAC system! There IS a difference in heat from full cold to full hot, but it is weak. The heat is like dog breath (minus the stink). Not enough to stay comfortable that's for sure.

    Fixes thus far:
    - I found the coolant hoses running to the heater core were dead cold and the aluminum pipes they attach to were also cold up to half way through. I removed the hoses and blasted them with water and now they flow well. The heater core hoses were still cool though, but at that point there was a tiny bit of heat in the cabin.
    - Today I flushed the heater core and now the hoses going to the core through the firewall are piping hot, but the heat in the cabin has only improved by a couple degrees. Perhaps the heater core is partially clogged and is only heating in a certain area? The water flow through the core seemed to be pretty good from what I could tell.

    Operation notes:
    - When the fan is set to "4" the air from the vent is barely warmed. At fan setting "1" there is noticeable heat from the vents.
    - This heat issue persists across all vent settings except in the AC settings where the temperature drops a bit.
    - The heat can indeed be adjusted from cold to hot and the cold is indeed cold, but the hot is just lukewarm. There is a difference in the sound of the airflow between the hot setting and the cold setting, so something is happening in there.
    - Temperature gauge on the cluster is dead on center. The engine seems to be heating properly. Upper rad hose is hot.

    Conjecture and Questions:
    - I would *guess* that the heater blend door actuator is possibly malfunctioning, or maybe it is the blend door? Could the blend doors be broken? Do the blend doors on the KJ break often like they reportedly do on the WJ?

    PS:
    Thanks in advance for any help! I'm pretty excited about this Jeep. I bought it on a whim and thought it was a bit puffy and silly at first, but after digging into it a bit I'm really stoked on this thing actually. I'm coming from owning an E36 BMW (my current daily) and a Mini Cooper, so this is a real strange beast to me and I can't believe how beefy it is built! I found the build sheet for my KJ amongst the service records and was super stoked to see it has the tow package and the Trac-Lok LSD! I've got a whole bunch of parts on order to refresh all the fluids and basic maintenance stuff. Hoping to get this thing reliable enough to go off into the forest this summer! Lots of cleaning to do too and I'll be repainting the rims bronze.
     

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    Last edited: Feb 22, 2021 at 2:22 AM
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  2. LibertyTC

    LibertyTC Well-Known Member Staff Member Moderator

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    Welcome, Nice Jeep. It it an 04?
    Hope there is nothing wrong with the blend door, you may just have trapped air..
    Lower rad hose & new thermostat installed yet? Use This one only.
    [​IMG]
    [​IMG]

    With the cooling system now flushed, try bleeding the air out when hot.
    Downward force, counterclockwise a bit, and paper towels handy, let it leak out a bit, til no bubbles seen/ then close/ tighten it.
    Don't use an allen key. It's hard to break free.
    [​IMG]
    Cold in the AM overnight, fill to the middle of reservoir tank/cold line.
    Monitor for a few days & only use HOAT or Zerex G-05 coolant !
    Kj' Jeeps have plastic water pump impellers, never use the wrong coolants.

    Do you have the owners manual ? Looked in the glove box up top for it? Good reference for fluid + specifications.
    Once I know what year your Jeep is, will get you the pdf online Factory service manual.

    Trac-Lok rear diff requires adding a 4 oz bottle of Mopar Limited slip additive.
    I use Lucas Dino (not synthetic) gear lube + the 4 oz bottle.
    [​IMG]
     
  3. WheelNut

    WheelNut New Member

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    Thanks so much Liberty-TC! That is a great collection of tips. Sorry, I should have posted the year! 2002 I do have the owner's manual, the '02 FSM, and the '03 parts list (couldn't find '02 parts guide). I have not yet changed the thermostat or lower rad hose yet. I'll order those up today. My bleed port seems to be stripped. I'll get the old one out somehow and install it along with the T-stat.

    I ordered Redline 75W140 synthetic with friction modifier already in it. I thought about the Mopar stuff, so hopefully this Redline will be okay.

    Mopar PCV is on the way, as is new belt tensioner, new rad cap, new belt, new air filter, new rear glass struts, new front prop shaft, Jeep adapter for the Motive brake bleeder, and...I think that's about it right now haha. Lots more little things to do and diagnose coming still.
     
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  4. LibertyTC

    LibertyTC Well-Known Member Staff Member Moderator

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    For now I'd leave the stripped hex alone and focus on ensuring that your jeep does have the Mopar thermostat installed.
    It has the built in air bleed and will assist in hopefully getting you some decent heat soon.
    Sounds like you have done some home work, the 02 fiche is MIA, and the 03 is close enough.
    The rear diff fluid should be changed every 20k. It is best to use dino gear lube as it sticks best to gears, compared to synthetics.
    I have also have a trac-lok & the mopar 4 0z bottle works well.
    You should be just "fine with the red line" lol, as it has the friction modifier built in.
    Still consider dino gear oil next swap out & the 4 oz bottle.
    Keep up the good work & you will have a good KJ soon!
    How many miles or Km's on the Jeep now? Any rust?
     
  5. WheelNut

    WheelNut New Member

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    Thanks, I'm hoping to have this thing running great soon! Can't wait to drive it on some rocks :D

    It has 240,000km (150,000mi). The body is really in pretty decent shape. One big dent in the rocker panel and some minor rust on the bottoms of the doors. A bit of rust on the rear upper control arm triangle, but pretty darn clean overall. Vancouver is really easy on steel, so I'm lucky there. The Jeep was a owned by a guy who bought it off a friend who had to quickly move back to England and he didn't maintain it AT ALL. It was missing 2.5L of oil when I bought it, which certainly made me very afraid, but the engine sounds good, and his friend he bought it from maintained it well, so *fingers crossed* it'll be okay. I actually brought 2 quarts of oil with me for the test drive o_O The neglectful owner only had the Jeep for a year and put about 7,000km (5,000mi) on it.
     
  6. LibertyTC

    LibertyTC Well-Known Member Staff Member Moderator

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    Folks who don't maintain their jeeps, then allowing a low oil condition, are immediately placed on the naughty list. Good for you on topping it up !
    Great that it runs well, any smoke on start ups? Keep that oil & filter clean. It is the single most important lifeblood of an engine, as I'm sure you already know! ;)
    240km is not bad, & when it comes to cooling, ensure that the electric fan works well. When A/c is engaged the fan should be working.
    You should have a nice camping rig all set up for summer!
     
  7. tommudd

    tommudd Moderator Staff Member Moderator

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    Toss that synthetic crap back on the shelf
    Regular dino does much better in the diffs