How to Replace the Gear Oil in a Mercury Marine Outboard Engine
- 1). Remove the boat from the water and park its trailer on level ground. Place a chock behind the rearmost tire on one side of the trailer and in front of a tire on the opposite side of the trailer.
- 2). Lower the outboard with the trim/tile switch on the side of the outboard (if equipped) so that the anti-cavitation plate is level with the ground. Place a drain pan under the outboard's lower unit.
- 3). Remove the vent screw from the lower unit with a screwdriver, making certain the light blue gasket comes out with the screw.
- 4). Remove the gear oil drain plug (it's located beneath the vent screw) with a screwdriver. If the plug includes a magnet, use a clean shop towel to wipe the magnet clean of any metal filings.
- 5). Allow all of the gear oil to drain out. The used oil should be blue or brown in color and free from water. If you see a significant amount of water in the gear oil, or if the gear oil has the consistency of a milkshake, you have a possible seal failure and need to have your engine serviced by a trained Mercury technician.
- 6). Open a quart of gear oil, remove the foil seal and insert the gear lube pump. Thread the pump onto the bottle of oil until tight.
- 7). Remove the plastic cap from the end of the hose attached to the gear lube pump and thread it into the lower hole in the lower unit (the drain plug hole) until snug.
- 8). Pump the gear oil into the outboard by repeatedly pushing down on the top of the lube pump.
- 9). Repeat the previous three steps to pump more oil into the lower unit. Depending on your model, you may not need the entire second quart of oil. You will know your gear housing is full when a steady stream (not bubbles) of gear oil pours from the vent hole with each pump.
- 10
Reinstall the vent plug and its light blue gasket with a screwdriver. - 11
Unscrew the gear lube pump hose from the gear oil drain hole and quickly reinstall and tighten the gear oil screw. Wipe any gear oil from the gear housing with a shop towel.
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