How to Change the Lower Unit Lube in a Johnson 50 Boat Motor

A lower unit oil change doesn't mean crawling into cramped spaces.

When you think "lube" you probably think about changing motor oil. You might even think about the oil in the motor on your boat. You may not think about changing the lubrication in the lower unit on your Johnson 50 but once a year, or once every 100 hours -- when your owner's manual says it should be changed. If you have changed the oil in your car or truck, you'll find no challenge in changing the oil in your lower unit.

Things You'll Need

• Drain pan
• Screwdriver
• Plug gaskets
• Soft, clean cloth

Instructions

1. Ensure that the motor is vertical and not leaning to the left or right. Set a drain pan under the lower unit. Unscrew the drain/filler plug on the bottom of the gear housing with a standard slotted screwdriver.

2. Unscrew the oil level/vent plug on the lower unit. Put a new gasket on the vent plug and set it aside until you're ready for its re-installation. Allow the gear oil to drain from the lower unit.

3. Rub your fingers over the magnetic tip on the drain screw, feeling for metal particles. A small amount of metal dust is normal wear and expected; metal chips are not. Inspect the gear oil that's drained for a milky appearance indicating that water has penetrated the propeller shaft seal.

4. Insert the tip of the lubricant tube in the oil drain hole. Squeeze the lubricant tube until the oil begins to come out of the oil level/vent plug hole.

5. Screw the vent plug back into place and tighten with a screwdriver. Put a new gasket on the oil fill plug and screw the plug back into its hole. Wipe the excess oil from the exterior of the lower unit with a soft, clean cloth.

Tips & Warnings

• When working on your motor, disconnect the battery cable from the negative post of the battery by removing the nut from the battery post and lifting the cable from the post. Removing the negative battery cable isolates the electrical circuit from the boat's common ground, making it electrically safe to work on the boat's electrical or mechanical systems. Always use a 5/16-inch open-end wrench when removing the nut from the negative post of a marine battery. The positive post uses a 3/16-inch nut. If the lettering or cable color is obscured by dirt or oil, the 5/16-inch wrench won't fit on the positive post.

• Never remove the vent or filler plugs when the lower unit is hot. Expanded lubricant will be released through the hole

References

• "Johnson Repair Manual -- 2.5 to 250 HP Models, 2001-2009 -- 25-55 HP (737cc), 40/50 HP (815cc) EFI and 25-70 HP (913cc) -- Lower Unit/Gearcase Assembly -- Draining and Filling"; Seloc; 2009