How to Use a Small Amount of Oil in a Mercruiser Outdrive

The outdrive in a Mercruiser Inboard/Outboard boat propulsion system needs periodic oil changes to resist wear, tear and premature failure. Looking at the outdrive, one would think it would take a lot of gear oil to fill the inside cavity to the proper capacity. Actually, a complete oil change requires only 2 quarts of oil and is a simple job.

Things You'll Need

  • 2 quarts gear lube
  • Lower unit oil pump
  • Flat screwdriver
  • Drain pan
  • Oil rag
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Instructions

    • 1

      Depress the down button on the power trim mechanism until the lower unit is in the fully down position.

    • 2

      Position a drain pan under the lower unit to catch the oil you are removing.

    • 3

      Remove the vent plug on the upper part of the housing of the lower unit using a flat screwdriver.

    • 4

      Remove the drain plug on the propeller shaft housing of the lower unit using a flat screwdriver.

    • 5

      Allow the oil inside the lower unit to completely drain. Gear lube is a high-viscosity oil and will flow slowly, even at warm air temperatures. Allow at least an hour for all the old oil to drain away.

    • 6

      Thread the fitting on the end of the lower unit oil pump into the drain plug hole and attach the pump assembly onto a quart bottle of gear lube.

    • 7

      Pump the first quart of oil into the lower unit, then transfer the pump to the second bottle of gear lube.

    • 8

      Continue pumping gear lube into the lower unit and watch the vent hole. When the cavity inside the lower unit fills with oil to the point it starts oozing out the vent hole, stop pumping.

    • 9

      Replace the drain plug and vent hole plug.

    • 10

      Fill the oil-level reservoir bolted to the engine with a few ounces of gear lube to bring the level to the full mark on the bottle.

    • 11

      Wipe the exterior of the lower unit clean of residual oil.