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Oil leak from lower unit

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  • Oil leak from lower unit

    Mercury outboard 65 hp est. mid-1970's. I'm fairly new to working on outboards, but mechanically inclined. Trying to change LU gear oil, the marina guy said to use "flush" screw to pump in new oil while "vent" screw open. No old oil can out of the flush hole, and only got in about a third of the new gear oil. Closed the screws and later noticed oil leaking from the propeller, as well as from the water intake screens. First of all, how to get more gear oil in, and secondly, what has caused the leaks? What is the suggested repairs? Thanks.

  • #2
    Re: Oil leak from lower unit

    ok harv, the man told you wrong, the flush goes to the water pump base to flush the water pump and the engine.the lube you have leaking now has gone into the water pump , no damage caused. the gear lube plugs are the the one marked vent by the flush screw and the one on the front/bottom of the lower unit. remove those two screws and let the old lube drain, then refill with gearlube from the bottom /drain hole till it comes out the vent. then with new seal washers on the plugs install the vent screw then remove fill fitting[assume you are using small hand pump on quart bottle** and replace the drain plug.


    • #3
      Re: Oil leak from lower unit

      Leaks can occur from several locations. The most common being the vent and fill plugs. I'd do a good oil change and monitor the oil quality every trip until you find the leak if any. An actual seal/gasket leak can be detected by a vacuum/pressure test, but do the simple things first.Here is a good guide to a oil change. When done, I top up the vent screw hole with a squirt can full of LU oil until oil comes out. Let it come out of the vent screw until it seeks its own level.As johnkc says, be sure to use new plug gaskets every time!!! Click me
      Alias "schematic"


      • #4
        Re: Oil leak from lower unit

        OK John, have located the lower plug - thanks, that is a relief! Now, the oil that's in the water pump, will it completely expel - and is that why I saw oil coming out near the prop? Again, thanks.


        • #5
          Re: Oil leak from lower unit

          Hi Harv Yes your oil will drain on it's own, as John said no damage done. It might be a little messy down there for a while. Might want to keep a drip pan under it for a day or two.


          • #6
            Re: Oil leak from lower unit

            harv , go catch some fish , the oil in the water pump will dissapate after running for a few minutes.when you did the lube job you probably put in enough oil to fill the water tube then the lube went into the exhaust/cooling passage therefore it drained out the exhaust and thru the prop