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Please help troubleshoot the lower unit gear case has some black oil in it

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  • Please help troubleshoot the lower unit gear case has some black oil in it

    1993 Evinrude 30hp... I just bought old Lund fishing boat and when I changed the lower unit oil old gear oil came out was green at first then near the end of the draining a bunch of thin black oil suddenly came out... I am not a mechanic by any means... no visible leaks. Looks like the black oil that comes from the exhaust after running with a hose and earmuffs. ?

    I'm guessing I have a problem with a seal? Please advise. Thanks.
    Last edited by frankoooo; 06-01-2017, 07:19 AM.

  • #2
    ********************
    (Checking Gearcase For Leaks)
    (J.Reeves)

    Remove the large slotted drain/fill screw from the bottom of the gearcase and also the identical looking screw that will be located up near the cavitation plate in order to drain the gearlube.

    After all of the lubricant has drained, install one of the slotted screws, whichever your preference might be.

    Apply 7 to 12 pounds of air pressure to the open screw hole. Use a piece of rubber fuel line or something to create a tight air hose fit if you do not have a proper fitting.

    If a leak exists, that pressure should allow you to locate the leak by sound and/or sight.

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    • #3
      Leaks

      I am thinking the leak is where the eye can't see unless the lower unit is removed... if black type oil has gotten into the gear case, what does this mean?

      thanks

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      • #4
        Originally posted by frankoooo View Post
        I am thinking the leak is where the eye can't see unless the lower unit is removed... if black type oil has gotten into the gear case, what does this mean? thanks
        It could just possibly be that a slight bit of the old very black gear-case lube that was used at one time is still on the inner gear-case walls somewhere and there is actually no problem to cure. I'm inclined to think this is the case due to the fact that if a seal was leaking, lube would leak out at some point... and water would have been leaking in. This would have resulted in a milky looking substance... and such is not the case. You have stated that the gear-case lube for the major portion looked quite normal.

        In my 30+ years of experience, I have never encountered having the black sooty looking substance that lines the long inner exhaust housing walls to enter the gear-case of any engine.

        If it were me, I would simply refill the gear-case with the required HiVis 90w gear-case lube and check it at whatever intervals you're accustomed to. If the lube still looks like lube and is not milky... there are no leaks.

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        • #5
          based on my problem description is this a possibility?

          Could the black oil that was at the top of the gear box be burnt old dirty gear oil, as I understand that it has not been changed in years...? and the oil doesn't appear to be mixed with water?

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