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  1. #1

    Default 25 hp mercury/ Tips and gear oil weight for lower unit change?

    First time doing. Any thoughts?

  2. #2
    Master Chief Petty Officer
    Join Date
    May 2010

    Default Re: 25 hp mercury/ Tips and gear oil weight for lower unit change?

    Must use 80/90w MARINE grade. You'll need the connection hose the goes to the lower unit. You have to drain and then pump the new oil in and up from the bottom till it comes out the top.

  3. #3
    Fleet Admiral Texasmark's Avatar
    Join Date
    Dec 2005
    N. Texas, USA

    Default Re: 25 hp mercury/ Tips and gear oil weight for lower unit change?

    Go to Wally World and buy your self a quart of Quicksilver Marine Lower Unit oil in the package that has the pump, a fitting to fit your lower unit drain plug, and a pump to pump it in. Marine lower unit oil is more than just 80 or 80-90, or 80-140 hypoid gear oil. It is specifically developed for the marine environment to combat water contamination/rust problems with gear boxes that operate submerged in water. It has a special additive that makes it stick to the metal providing insulation between the metal and any water that leaks into the gear box.

    Put the engine in a vertical position.

    Unscrew the dime sized SS drain screw at the bottom of the lower unit gearbox bulge and the vent screw which is on the starboard (right side, curb side) just above the anti vent plate....the horizontal plate just above the prop,.

    Let the old oil drain out and if it is milky, or chocolate colored you have a leak in the LU that needs to be fixed.

    If not, and the fluid is blue black, connect the adapter to the drain hole, the pump to the quart bottle and the plastic hose interconnecting both.

    Pump the pump till you see fluid and some bubbles at the vent hole. Pump a little more to reduce the quantity of bubbles.

    Install the vent screw ensuring that it has a gasket.

    Remove the fill connector at the drain screw and install that screw also ensuring it has a gasket. Loosing a small amount of oil is normal.

    You are ready to go.

    If you are new to boating or have a new boat, a knowledgeable friend could show you how to operate your boat and save you a lot of grief, maybe some money, and maybe your life.

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