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Thread: Gear Oil contaminated or not

  1. #1
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    Default Gear Oil contaminated or not

    Gear Oil.jpg

    I have this residue in old gear oil. I left it in the jar for a few weeks to check because when I changed the oil it didn't look as uniform as I expected.

    It doesn't look like water but I'm not sure. I know there are some additives in marine gear oil but I don't expect they are supposed to be separated from the main oil.
    Any thoughts?
    Thank you!


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  3. #2
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    Contaminated. It should have nothing but the honey coloured oil in the jar.

  4. #3
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    Thanks.
    I guessed the same too, but what is that? It doesn’t look like water, is it?
    How would I determine what is that and where to look for a problem?

  5. #4
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    Quote Originally Posted by MarkD View Post
    Gear Oil.jpg

    I have this residue in old gear oil. I left it in the jar for a few weeks to check because when I changed the oil it didn't look as uniform as I expected.

    It doesn't look like water but I'm not sure. I know there are some additives in marine gear oil but I don't expect they are supposed to be separated from the main oil.
    Any thoughts?
    Thank you!

    Definitely contaminated. Check your seals. One of them is likely cracked and leaking. I have a Mercury 25 four stroke with a completely grenaded lower unit upper drive shaft bearing that's only 6 months out of warranty. The lower unit gear oil has been changed annually with the levels checked before launching last week for the first time since duck hunt last fall. It'll be interesting to see what happened with the bearing running dry.
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  6. #5
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    Water in the gear oil. Bad seal around prop shaft or if you have a bad pair of washers on the drain and fill bolts. Could be a loose bolt as well. Take it to a mechanic. They will pressure test the lower unit.

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    Quote Originally Posted by Fenelon View Post
    Water in the gear oil. Bad seal around prop shaft or if you have a bad pair of washers on the drain and fill bolts. Could be a loose bolt as well. Take it to a mechanic. They will pressure test the lower unit.
    Thanks Fenelon,but,that's already been done. Gear oil level is correct,winterizing was done properly (by me) with no evidence of leaks over the winter. Oil levels were re-checked before spring start run-up. Everything seemed in order before launch,but,10 minutes out,the main bearing seized locking everything up instantly. Sometimes,stuff just happens for no particular reason. I'm told that this happens very rarely with Merc's,but,it's quite common with Yamaha and Tohatsu. With the warranty expired,this one's gonna hurt.
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  8. #7
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    Marine oil has emulisifiers in it, when mixed with water this turns whitish and floats on water so it can be cleaned up from the environment in case of a leak into the lake.
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  9. #8
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    When in doubt ... change it out. Ideally there should be nothing but gear oil in there and not some milky mixture that's why it is most important to change the oil at the end of the year in case water did find a way in so that the water doesn't freeze and burst seals/casing etc.. Gear oil has two main functions , one as a lubricate and the other to transfer heat. Water will do the same thing but not as effectively. You may also want to put a magnet in the old oil to see if any metal is in it ? As for bad bearings ? It happens ! Not like manufacturers are using Swedish or German made when there is cheaper ones to buy ?
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  10. #9
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    Thanks a lot!
    I took some time trying to figure it out..
    I watched some youtube videos and was really surprised to see how one guy changed gear oil and found clear water, not emulsion, flushing from the hole.
    The thing is that I didnít change it at the end of the season (I know itís wrong) and changed it recently prior to putting the boat into the water. Even if there is water, still no full separation occurred, as you can see. The sediment is still a sort of emulsion, not clear water.
    My main concern is the slightly gray color, as I read that this is a bad thing, worse than just whitish milky color.
    I then put the same oil in the jar, added some water and agitated it at high RPM for Ĺ hour.. Now, after four days it is still emulsion, no separation occurs.
    The motor is relatively new, I bought it in 2018 (oh, well, not so new, the time passes really fastÖ), it is a Tohatsu 20 HP, made in Japan.
    My plan now is to make several outings and drain the oil. If there is something wrong again Iíll probably need to do a pressure test.
    Iím planning to deal with it myself, bringing the boat to the marine for service is not an option for me.

  11. #10
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    Quote Originally Posted by MarkD View Post
    Thanks a lot!
    I took some time trying to figure it out..
    I watched some youtube videos and was really surprised to see how one guy changed gear oil and found clear water, not emulsion, flushing from the hole.
    The thing is that I didn’t change it at the end of the season (I know it’s wrong) and changed it recently prior to putting the boat into the water. Even if there is water, still no full separation occurred, as you can see. The sediment is still a sort of emulsion, not clear water.
    My main concern is the slightly gray color, as I read that this is a bad thing, worse than just whitish milky color.
    I then put the same oil in the jar, added some water and agitated it at high RPM for Ĺ hour.. Now, after four days it is still emulsion, no separation occurs.
    The motor is relatively new, I bought it in 2018 (oh, well, not so new, the time passes really fast…), it is a Tohatsu 20 HP, made in Japan.
    My plan now is to make several outings and drain the oil. If there is something wrong again I’ll probably need to do a pressure test.
    I’m planning to deal with it myself, bringing the boat to the marine for service is not an option for me.
    IMO -
    - The slightly grey vs milky white doesn't make a big difference.
    - You won't get the oil / contaminant to separate. It's not supposed to.

    My 2001 mercury 25hp - bought new - always had milky looking (now grey) gear lube when I changed it.
    It is important to change the gear lube when you put the boat away in the fall, not when you take it out in the spring.

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