Oil leak - rear main seal?

Discussion in 'KJ General Discussion' started by Royy, Jan 29, 2019.

  1. Royy

    Royy Full Access Member

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    Just a bit of background - my 2005 3.7 KJ has been going through a lot of oil for quite a while. Approximately a year ago I replaced the oil pressure sender and the front main seal, because both were leaking. That, and upgrading to the 2006 PCV system reduced the amount of oil it goes through, but it's still a lot. I'd estimate it's about a quart per 300-400 miles.

    There's a lot of almost impossible to remove grime and old oil on (mainly) the bottom of the front diff (from those old leaks, I assumed), but I never saw any really wet spots there, and never noticed any drips. I thought the engine was simply burning all the oil it's going through.

    Today, while changing the front differential fluid, I noticed wet oil on the bottom of the front differential, and the part of the transmission crossmember directly behind the diff. It was definitely engine oil, not gear oil from the diff.

    I can't see where exactly it's coming from, but it covers pretty much the entire front diff, and from there gets blown back onto the trans crossmember.
    Everything up front is dry. I checked the valve covers, oil pressure sender, oil filter, front main seal - nothing leaking there. The inside of the inspection cover is dry (I did not take it off, but stuck some paper towels in there and they came out dry), and the plastic channel thingy that lead from the oil filter to the rear of the engine is dry as well. So I'm pretty sure the oil is not coming from the front of the engine. No wet spots on the oil pan either.

    Does it sound like this could be a rear main seal leak? I know those are not common on the 3.7, but at this point I have no clue what else it could be.

    [​IMG]
     
  2. J33Pfan

    J33Pfan Full Access Member

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    Check the valve covers. Leaks get tricky
     
  3. Royy

    Royy Full Access Member

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    That was one of the first things I checked, they are both completely dry.
     
  4. Conundrum2006

    Conundrum2006 Full Access Member

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    could it be blow back from leaking CCV? Crank case ventilation.





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  5. Royy

    Royy Full Access Member

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    All the PCV hoses are fine, no leaks. And there's no oil anywhere on top of the engine, just the bottom.
     
  6. tommudd

    tommudd Moderator Staff Member Moderator

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    First thing I would do is clean all the gunk off the area, spray well with cleaner, hose off with high pressure hose and then watch daily
    The way it is, hard to say/ tell
     
  7. Conundrum2006

    Conundrum2006 Full Access Member

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    If the pcv were clogged it could cause leaks in unusual places, not sure about the 3.7. On other engines I know clogged pcv can creat a situation where oil leaks happen at the rear main, but these were much older engine.

    IMO nobody wants to say go on a big job like this because With these engines it’s rare to get rear main leak, add oil pan gasket leaks to that list too. Oil pan rusted through is another story, pan gasket is a PITA to remove with the engine out of the Jeep.

    If it were my Jeep I would check everything else first, clean up the affected areas and see where the fresh oil sign is coming from.



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  8. dude1116

    dude1116 Full Access Member

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    I have the same leak and I've replaced nearly everything. Although I'm not using as much oil as you are.

    Valve covers 2x each, front seal, rear seal while my trans was out...trans shop told me it was moist but not bad, and oil pressure unit which I'm still suspicious of because I used a cheap part.

    I know my oil filler gasket is pretty bad so that can be a spot to check as well. Last thing to check would be the oil pan gasket which requires serious labor to change out.
     
  9. Royy

    Royy Full Access Member

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    I finally got around to removing the structural cover, and everything was clean underneath there. So (unless I'm missing something), I think that rules out the rear main seal.

    There was lots of fresh oil all over the bottom again. I checked the valve covers, oil filter, oil pressure sender, PCV valve and hoses, front main seal... all completely dry. So, that leaves the oil pan gasket... :eek:. I tightened all bolts on the pan that I could reach. Hopefully that at least slows the leak down somewhat. This is going to be a real pain to fix.
     
  10. Aloicious

    Aloicious New Member

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    Did you check the crank sensor? Ive had an oil leak there, it shouldn't leak a lot from there, but an easy thing to check and you can look around the pan seal while you're down there. Otherwise it sounds like the oil pan to me. I feel your pain on that, I just went through changing it too.
     
  11. Royy

    Royy Full Access Member

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    Crank sensor is completely dry.

    I just did an oil change. Despite adding a quart every 300-350 miles, only about 3 quarts came out. Ugh. Losing that much, I just don't get how there are never any drips when I park it.
    I cleaned the bottom up as much as possible, and covered the seam between the oil pan and the bottom of the engine with black gasket maker (at least, in all the spots where I could get to it without taking the entire Jeep apart). Hopefully that'll seal up some of the leaking spots temporarily. Also switched to a heavier oil.
    It's just a band-aid fix, but hopefully it will at least slow the leak down somewhat until I can fix it properly.
     
  12. Aloicious

    Aloicious New Member

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    Another possibility is a timing chain cover leak, I think i have a small timing chain cover leak on my 05 but its its not bad enough to fix right now.
     
  13. Aloicious

    Aloicious New Member

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    My recent situation was similar to yours though maybe not as bad. I was adding a quart every 500-750 miles, no dripping while parked but lots of oily grime buildup and wet spots.

    I had known wet leaks on the front of the passenger valve cover, pressure sending unit, and crank sensor. With weeping around the oil pan gasket, and sponge bob was soaked in oil so suspect pcv problem.

    I replaced the following gaskets while also doing some other unrelated work: valve cover, oil pressure sending unit, crank sensor, oil pan, front main, oil fill tube. I also upgraded to the 07 style pcv system and replaced spongebob.

    Since then i have one spot on one part of the timing chain cover that is still weeping but everything else is dry and i have only had to top off maybe .5 quarts in the past 1500ish miles.

    Also, are you burning any? Bad valve seals and/piston rings could be contributing to the oil loss as well.