How to Change the Lower Unit Gear Oil on a 4.3 MerCruiser

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    Changing Lower-End Gear Oil

    • 1). Locate the gear oil drain screw and the oil level plug on the motor. When looking at the boat from the rear end, look on the right side of the motor toward the very bottom. The gear oil drain screw will be the Allen screw furthest down, while the oil level plug will normally be approximately halfway up the lower end, and is also an Allen screw.

    • 2). Place the drain pan underneath the lower end, with the motor sitting fully vertical. Unscrew the oil level plug and the oil drain plug. Allow the oil to drain fully out of the lower end.

    • 3). Load the pressurized gear oil filling container with the gear oil. Many of these pumps have a screw-in attachment. Attach the pump to the gear oil drain plug housing, and begin pumping the gear oil into the motor. Continue pumping until the new oil begins to flow out of the oil level plug. Replace the oil level plug and remove the pump from the lower end. Replace the drain plug and wipe any oil off of the lower end.

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