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Thread: Black Lower Unit Oil?

  1. #1

    Default Black Lower Unit Oil?

    Hi Guys, I did my 100 hour maintenance on my Yamaha 150 outboards last night and replaced the oil in the lower units. The oil from the lower unit of the starboard engine was fairly clean and almost new appearing. The oil from the lower unit of the port engine was absolutely black, almost like engine oil that had been neglected for several years but these are newish engines. There are no signs of leaks and there was no evidence of water contamination, etc.

    Operation including shifting is completely normal as far as I can tell. Any thoughts? Should I be concerned?

    Thanks so much!
    "Miss Mary"
    Kingfisher 2725, twin Yamaha 150's

  2. #2
    Member hoose35's Avatar
    Join Date
    Jul 2008
    Soldotna, Alaska, United States


    I would contact Yamaha and see what they have to say. Seems strange to me
    Responsible Conservation > Political Allocation

  3. #3
    Member jrogers's Avatar
    Join Date
    Apr 2006


    I think it is a heat issue. Be careful about what Yamaha says (or any manufacture). My experience is that they say it is no big deal, and then when it blows up outside of warranty, it will be tough luck. When you have two side by side with different results, I would say it is worth having the dark oil one torn down by someone good before you have a big failure. You can also have an oil analysis done on it to tell what type of metal is in it which may give a clue about what is failing. Also look closely at the paint and covers on the motor to see if you see any signs of heat. After mine failed, I noticed crinkled paint, which was not a factory finish, but a sign of a bearing getting hot.
    2009 Seawolf 31'
    Fully Loaded

  4. #4


    jrogers, this is pure gold (black gold that is! hehe) I hadn't thought of heat issues and I bet you're exactly right. I'll get it checked asap. Thanks so much!!
    "Miss Mary"
    Kingfisher 2725, twin Yamaha 150's


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