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  1. #1
    Member Hez's Avatar
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    New Drain Screw + New Gasket + Old Gasket = Water in Lower Unit - Advice please

    1996 Mariner 175 Magnum EFI - Serial OG360900

    Got the boat and motor about a month ago. Changed the lower unit gear oil and replaced the drain screw, vent screw and both gaskets around screws.

    Afterwards, got to thinking that I had 2 old screws but only 1 old gasket. I guess I assumed it fell out and I didn't notice it.

    3 weeks later (after running the boat about 5 times...never any runs longer than about 10 minutes at a time...maybe 2 hours total on the motor) I check the lower unit oil and notice it is extremely dark with a little discoloration.

    I immediately drain the oil and begin investigating.

    That's when I find the old gasket in the drain plug under the new gasket. So obviously this is where some water got in.

    I removed the old gasket and all pieces of it and cleaned off the new gasket good. Cleaned the hole, and made sure there were no pieces there - then re-filled the lower unit with oil.

    I have not ran it yet.

    Had planned to run it, then drain the oil again and re-fill it with new gear oil, and then depending on what kind of shape the drained oil was in - go from there.



    Is this the proper procedure?

    Hopefully I caught it before it caused any damage.

    Any advice is welcome, thanks.

    Wishin' I was fishin'...


    1990 Ranger 374v
    1996 175 HP Mariner - Magnum EFI
    25p Tempest - A45 model
    80 lb 24v MinnKota Maxxum
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  2. Member DrewFlu33's Avatar
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    #2
    Sounds to me like you caught it in time! I think where you really run into trouble is when the water intrusion gets to the point that the lower unit oil looks lighter and milky colored. If you didn't find any metal shavings in the drained oil, I'd bet you're in good shape.

    As far as your procedure, I'm all but certain what you're doing is going to work out just fine. In fact, I'm not sure I'd personally even go as far as to drain/replace it again. Overkill and an abundance of caution with these things is never a bad idea, but given my propensity towards carelessness at times I'd be more worried I'd mess up when changing the oil that final time and end up with another issue. I'm also thinking that removing and reinstalling the screws again puts unnecessary wear on your new gaskets, though I'm sure age more than "use" is the biggest enemy of those.

    Maybe just drop the motor down while the boat is on the trailer and stick a couple white paper towels under it? If there's any leakage at all to be concerned about after you took care of removing the old gasket and installing the new one properly and refilling with fresh oil, I've got to believe you'd see evidence on those paper towels after a day or two. If you've got clean paper towels after that, my inclination is that you're good to go.
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  3. Member Hez's Avatar
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    #3
    Thanks for the response.

    I really appreciate the feedback.

    I feel just about the same way you do - "All will be fine, I caught it in time..." was just looking for some affirmation from someone a little more experienced.

    Wishin' I was fishin'...


    1990 Ranger 374v
    1996 175 HP Mariner - Magnum EFI
    25p Tempest - A45 model
    80 lb 24v MinnKota Maxxum
    Humminbird Helix 10
    Humminbird Helix 7
    Garmin EchoMap 106sv w/ LS
    Dual 8' Power Poles



  4. Member
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    #4
    If you want to really make sure it's good to go have it pressure tested.

  5. Member
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    #5
    You mentioned "discolored". What did the OLD oil look like? Possible you are just mixing old oil and new, since you can't drain 100%. If old oil was dark, you might just be seeing the mixed result? Best check for water is to let it sit for a day, trim all the way down and remove just the lower drain screw. If there's water, it will drop out first since it is heavier than the oil. You do have to wait a while after running since the gears will emulsify the water/oil making it harder to see a tiny bit of intrusion. I've had plenty of water intrusion issues over the years (former racer here). Never saw the oil turn really dark from water mixed in. Usually a creamy look right after running, then it pretty well separates given some time. Was there any water in the original oil you removed? If so, I'd be checking all the usual suspects. Propshaft seals, bearing carrier o-ring (and verifying the big cover nut is torqued correctly), and then the seals on the other end as well, drive shaft and shift shaft. Pressure test is easy to do. Pretty easy to build a pressure tester with a gauge, a hand-pump of some sort (bicycle, football, etc) plus a trip to the local auto parts store to find the right fitting for a drain plug opening, tubing, and a T so you can hook pump, gauge and the drain fitting all into the same closed circuit.

    WHOLE lot easier than dropping the lower unit and trying a visual inspection which is often not going to work.
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  6. Member Hez's Avatar
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    #6
    Quote Originally Posted by OldTimer57 View Post
    You mentioned "discolored". What did the OLD oil look like? Possible you are just mixing old oil and new, since you can't drain 100%. If old oil was dark, you might just be seeing the mixed result? Best check for water is to let it sit for a day, trim all the way down and remove just the lower drain screw. If there's water, it will drop out first since it is heavier than the oil. You do have to wait a while after running since the gears will emulsify the water/oil making it harder to see a tiny bit of intrusion. I've had plenty of water intrusion issues over the years (former racer here). Never saw the oil turn really dark from water mixed in. Usually a creamy look right after running, then it pretty well separates given some time. Was there any water in the original oil you removed? If so, I'd be checking all the usual suspects. Propshaft seals, bearing carrier o-ring (and verifying the big cover nut is torqued correctly), and then the seals on the other end as well, drive shaft and shift shaft. Pressure test is easy to do. Pretty easy to build a pressure tester with a gauge, a hand-pump of some sort (bicycle, football, etc) plus a trip to the local auto parts store to find the right fitting for a drain plug opening, tubing, and a T so you can hook pump, gauge and the drain fitting all into the same closed circuit.
    WHOLE lot easier than dropping the lower unit and trying a visual inspection which is often not going to work.
    Thanks for the reply.

    Old oil that I drained out about 3 weeks ago was dark black. No discoloration other than being black. I re-filled with quicksilver gear oil that is bluish in color, and when I drained it this time - it was black with a milky white streak. I then poured some fresh gear oil in a glass jar and added a little bit of water - it then began to turn dark as well (not the coffee/cream color that I would have suspected also) although it did separate.

    There was no water in the oil I removed 3 weeks ago.

    I am going to run it this weekend, pull the drain screw and do a visual check of the gear oil then - if I see anything other than blue gear oil, I will drain it completely and start with a pressure test, as has been suggested.

    Hoping that the double screw gasket around drain plug was the culprit.

    Some lessons are learnt best the hard way
    Last edited by Hez; 07-20-2017 at 07:16 PM.

    Wishin' I was fishin'...


    1990 Ranger 374v
    1996 175 HP Mariner - Magnum EFI
    25p Tempest - A45 model
    80 lb 24v MinnKota Maxxum
    Humminbird Helix 10
    Humminbird Helix 7
    Garmin EchoMap 106sv w/ LS
    Dual 8' Power Poles



  7. Member Hez's Avatar
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    #7
    Ran her pretty good today and checked the LU oil when I got home. No water...and looked just as blue as when I put it in.

    Wishin' I was fishin'...


    1990 Ranger 374v
    1996 175 HP Mariner - Magnum EFI
    25p Tempest - A45 model
    80 lb 24v MinnKota Maxxum
    Humminbird Helix 10
    Humminbird Helix 7
    Garmin EchoMap 106sv w/ LS
    Dual 8' Power Poles