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Thread: Jeep Wrangler 3.8L Engine Thermostat Replacement

  1. #1
    Meme King WJCO's Avatar
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    Jeep Wrangler 3.8L Engine Thermostat Replacement

    I couldn't find a write-up on this so hopefully I didn't duplicate one. Either way, we had coolant leaking between the plastic and aluminum at the thermostat housing. I've seen enough housings warp and crack, I opted to replace the housing itself while I had it all apart. Make sure the engine is cold when this repair is done.

    Parts needed:

    Thermostat: MOPAR 68210220AA
    Housing: MOPAR 04666149AA
    Correct coolant

    I found several different Mopar thermostat part numbers online so I hope this one ended up being the correct one. It looks pretty much the same and opened correctly when I was all done. I did order it from a dealership. I was a little surprised when I got it that the brand listed on it was MotoRad. I spent some time doing some research and found that several Jeep dealers sell MotoRad thermostats as an OEM equivalent

    DSC01815.jpg

    Tools needed:

    5/16" nut driver (or socket and ratchet)
    10mm box end wrench
    10 mm gear wrench (optional)
    Channel locks





    So here's what we started with:

    DSC01820.jpg

    As stated earlier, make sure the engine is cool when doing this repair!

    Use a 5/16" nut driver to remove the air inlet hose between the air filter and throttle body. There will be two hose clamps that need to be loosened. Then take it off and move it out of the way.

    DSC01822.jpg

    DSC01823.jpg


    Remove the connector at the throttle body motor. Be very careful that it doesn't break. The connector will be old and brittle. Then move it out of the way to the side.

    DSC01824.JPG

    Here you can get a good working area of the tstat housing with no obstructions.

    DSC01825.jpg

    At this point, the coolant will need to be partially drained. This can either be done underneath at the bottom of the radiator or it can be drained right at the thermostat housing during the repair. I opted to just remove the thermostat housing and let the coolant drain from this location. I had a drain catch pan under the front of the motor to minimize the mess of coolant on the floor.

    To remove the housing, there are two bolts with a 10mm head. A gearwrench or socket will speed things up, but I couldn't get either on the back bolt and had to use a regular 10mm closed-end wrench. Luckily, once they're loose, they can be spun out the rest of the way with your fingers.

    DSC01826.jpg

    DSC01827.jpg

    Lift up on the housing while twisting it back and forth a little and it will come loose and coolant will drain.

    DSC01828.JPG

    Move the upper radiator hose abrasion sleeve toward the front of the Jeep and away from the clamp. Then use some channel locks to collapse the spring clamp and move it upward on the hose out of the way. Then you will have to really pull and twist the thermostat housing to break it free from the hose.

    DSC01830.jpg

    It was quickly obvious that our thermostat gasket was what failed on ours and caused the leak.

    DSC01842.jpg

    Because this style thermostat uses a rubber oring, there shouldn't be any gasket stuck to the aluminum part of the housing, but ours had some crud and build up so we used a gasket scraper to clean it really well. We then used a rag with BrakeClean to get it as clean as possible.

    DSC01833.jpg

    I laid the old parts next to the new parts. I've always gotten in the habit of leaving thermostats in the housing until I have the new part installed. This way there is no confusion as to which way the thermostat goes and it doesn't get accidentally installed backwards. The gasket should already be installed on the new thermostat. When installing it in the new housing, pay close attention to the air jiggle valve and make sure it goes in the same position as the old one. Make sure the thermostat/gasket assembly is pressed down so the seal is even looking on all sides with no distortions.

    DSC01834.jpg

    Then install the entire assembly back on to the engine and torque the bolts to spec. According to the Project JK torque specs, these should be 105 INCH POUNDS. Do not over-torque them or you could crack the new plastic housing. Make sure to go back and forth between the bolts so they are torqued evenly.

    DSC01837.JPG

    Re-install the throttle body motor connector making sure it clicks firmly in place.

    DSC01838.jpg

    Then place your upper radiator hose onto your new thermostat housing and use channel locks to move the spring clamp back into place. If your wiring loom is like mine, it crumbled in several places during the repair, so I opted to put new wiring loom on 3 different wires shown on the arrows below.

    DSC01839.jpg

    Reinstall the air inlet tube and tighten both clamps.

    DSC01840.jpg

    Then fill up the radiator with the proper coolant and squeeze the upper radiator hose several times to burp the air out. Then add more coolant as the level drops until it is full. Start the vehicle and run it until the thermostat opens and continue topping off the coolant until it stays full. Once the thermostat is open and level is full, put the radiator cap back on and tighten it properly.

    DSC01844.jpg

    Along with the step above, to know when the thermostat is open, the coolant level will drop a little. Along with that, a laser thermometer is a good tool to use. Checking the temperature on both sides of the thermostat will also show. When I first started, the plastic part along with the radiator hose were at about 50F. Once the thermostat opens, the hot coolant rushes upward and the temperatures will read much warmer.
    DSC01848.jpg

    Make sure to keep an eye on the dash temperature gauge to make sure the vehicle isn't overheating. Also make sure your heat is blowing hot inside to ensure cooling system is working properly.

    DSC01851.JPG

    To ensure all of the air is bled out of the cooling system, check the level over the next few days and squeeze the upper hose and add coolant as needed. MAKE SURE ENGINE IS COLD WHEN YOU CHECK THE COOLANT LEVEL !!

    That's it.
    Last edited by WJCO; 03-13-2019 at 12:41 PM.
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  2. #2
    Old Timer Andy5160's Avatar
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    Great write up man you were saying We did this and that who helped you ?


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  3. #3
    Meme King WJCO's Avatar
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    Quote Originally Posted by Andy5160 View Post
    Great write up man you were saying We did this and that who helped you ?


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    Thanks. My oldest son helped. He's only 6 but not too early to learn this stuff.

    As far as 'we,' just because my name's on the title, I still refuse to claim overship of the wife's Jeep
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  4. #4
    Old Timer Andy5160's Avatar
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    Quote Originally Posted by WJCO View Post
    Thanks. My oldest son helped. He's only 6 but not too early to learn this stuff.

    As far as 'we,' just because my name's on the title, I still refuse to claim overship of the wife's Jeep
    I have 6 years old as well it is truth that is not too early and hey We gotta Compromise somewhere


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  5. #5
    Nothing but a Thing nbunga's Avatar
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    Nope, never too early. My oldest is 6 also. He’s gotten pretty good at getting his little hands in places and putting nuts on bolts for me.

  6. #6
    Addict catahoula's Avatar
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    Nice write up I might need someday!
    “Dogs are our link to paradise. They don't know evil or jealousy or discontent. To sit with a dog on a hillside on a glorious afternoon is to be back in Eden, where doing nothing was not boring--it was peace.”

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  7. #7
    Meme King WJCO's Avatar
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    Quote Originally Posted by catahoula View Post
    Nice write up I might need someday!
    Thanks.

    So the Jeep got about 100 miles on it today with no issues. I know it's too soon to be too sure, but this 'MotoRad' thermostat seems to be doing its job.
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  8. #8
    Fresh Catch Chapco's Avatar
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    Great Write Up! This took me about 15 minutes. Much easier on the 2007 then later models.
    My thermostat was broken off on one side of the spring.

  9. #9
    Meme King WJCO's Avatar
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    Quote Originally Posted by Chapco View Post
    Great Write Up! This took me about 15 minutes. Much easier on the 2007 then later models.
    My thermostat was broken off on one side of the spring.
    Sweet. Glad it helped. Ours has been fine since the repair. Did your new thermostat happen to be one of those MotoRad ones?
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