How to Change Gear Case Oil in Outboard Motors


Annual maintenance of your outboard motor is important. One of the most important maintenance tasks is to drain and refill the lower unit, or gear case. Changing the gear case oil removes any water which might have gotten in and allows the oil to be examined for metal and other indicators of a potential problem.

Things You'll Need

  • Large screwdriver
  • Outboard motor lower unit oil
  • Drain pan
  • Position the motor in the down position and place the drain pan under the lower unit.

  • Place a container under the motor to catch the old oil, then remove the lower unit drain screw, which is located on the bottom of the gear case "pod" at the base of the motor.

  • Remove the lower unit vent screw, located near the midpoint of the lower unit.

  • Refill the lower unit gear case by forcing oil through the drain screw hole until it comes out of the vent hole. Specialized pumps are available for this, but a plastic squeeze bottle with a tapered nozzle cap (such as from a ketchup dispenser bottle)works fine. Simply force the cap into the hole and squeeze the bottle, forcing the oil in. You may need a helper for this if your lower unit holds more than one bottle of oil. The helper can refill the bottle while you plug the hole.

  • Quickly replace the drain screw when the lower unit is full (oil comes out the vent hole). Tighten the screw firmly.

  • Inject oil in the vent hole to replace any oil that drained out while the screw was replaced.

  • Replace the vent screw and tighten securely.

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