25 hp Mercury Lower Unit

Discussion in 'Bubba's Outboards' started by randallewis, Mar 28, 2008.

  1. randallewis

    randallewis New Member

    Messages:
    415
    State:
    Louisiana --Shreveport
    I have a 2002 25 hp merc. ser#0T569650. I noticed a few drops of black oil on the driveway below the lower unit. I checked the oil in the lower unit. It was low and milky but I didn't find any water. The oil in the lower unit was not the same color as on the driveway. I drained it and added new oil and ran it about 30 min. It was full but milky and hasn't leaked any oil. I was told the lower unit would have to be pulled and a seal kit installed. Is this a big project like special tools?
     
  2. fishnfwl

    fishnfwl New Member

    Messages:
    3,334
    State:
    South Cent
    Randal, can you tell where it is leaking from? does it seem to be coming from the prop area or maybe below where the filler plugs are? I would say to 1st make sure that your O-rings on your filler plugs are in good shape, I have the same engine and had the same last fall and all mine was was a bad gasket ring around the filler/drain hole. Already had some of them in the shop so it was a very easy fix, (for once).
    Randy
     

  3. Wabash River Bear

    Wabash River Bear New Member

    Messages:
    3,019
    State:
    Indiana
    It sounds like unburnt premix oil coming from the exhaust through the prop. You can pull the prop and see if its coming from the exhaust port. It would also be a good opertunity to clean out any debri ( fishing line, weed material, ect) from your prop shaft, and grease the prop shaft. Mine does this and is normal for a two stroke. Bubba will be along to give you a pro's take on your situation. Good luck.
     
  4. fishnfwl

    fishnfwl New Member

    Messages:
    3,334
    State:
    South Cent
    Yes this is true but wouldn't cause the milky oil?
     
  5. randallewis

    randallewis New Member

    Messages:
    415
    State:
    Louisiana --Shreveport
    The black oil is coming from inside the housing when I removed the prop. The oil was milky from the lower unit but I'm not sure I flushed it good. Would it hurt to flush it w/ diesel then add new oil?
     
  6. fishnfwl

    fishnfwl New Member

    Messages:
    3,334
    State:
    South Cent
    Is this your lower unit? I am also interested just to "know" in advance. 25 hp merc.

    [​IMG]
     
  7. Wabash River Bear

    Wabash River Bear New Member

    Messages:
    3,019
    State:
    Indiana
    No, but I think we are talking about two differt things here. The black oil coming from the prop area of the lower unit is what I was referring to. The milky looking oil in the lower unit is probably just aerated oil since he said he just changed it then ran it. A good way to tell is to drain it out into a clear glass and let it settle out. If its water it will seperate into two layers. If its aerated, the air will settle up and leave the oil.
     
  8. fishnfwl

    fishnfwl New Member

    Messages:
    3,334
    State:
    South Cent
    Well with that being said I don't see what that would hurt? and it may be just what WRB stated if there was some water left in it, but it still had to get there the first time?
     
  9. fishnfwl

    fishnfwl New Member

    Messages:
    3,334
    State:
    South Cent
    YES OK I see what you are saying, makes sense to me.....
     
  10. Wabash River Bear

    Wabash River Bear New Member

    Messages:
    3,019
    State:
    Indiana
    A good way to test the integrity of the seals in your lower unit is to pressure, or vacume test it. Do a google search "pressure testing an outboard lower unit", you will get many results.
     
  11. randallewis

    randallewis New Member

    Messages:
    415
    State:
    Louisiana --Shreveport
    Randy I don't know if that schematic is mine or not. Looks like it could be.

    Bear I'm going to run it about 4 hrs then drain it in a glass. I haven't seen any free water yet. Its hard to get on the water down here w/ these 25/30 mph winds.
     
  12. Bubbakat

    Bubbakat New Member

    Messages:
    4,532
    State:
    McMinnvill
    Randal that oil coming through the prop area is unburned fuel. This is common an outboard won't burn all the oil is ingests. The milky oil in the lower unit is water intrusion. Change it out and put some new gaskets behind those fill and drain screws. That is the most common place to start when you have water in there. It will need to be changed a couple times to get the water out but be sure to put in new gaskets behind those screws.