Lower Unit Lube

Changing Your Lower Unit Lube

by Conrad & Judy Kreuter

Is it time to change your lower unit lube? How, you ask, do I do this without making myself a candidate for the hot oil wresting tournament? Most outboard and stern drive manufacturers suggest changing lower unit lube oil every 50 to 100 hours or at least once per season. So this is not a job you can put off until another day.

If your motor is brand new, the lower unit lube should be changed during the first 10 to 20 hours of use. Most new engines have a special break-in lubricant especially for this purpose. This procedure should be done by an authorized service center. The mechanic will also check the lube for metal particles, which indicates excessive wear during the break-in period and may require additional repair.

For a routine gear oil change, grab a container of sufficient capacity to hold the old gear oil. (Don't be like our nephew who used his wife's good Tupperware container!) Make sure the container can be placed under the lower unit in order to catch all of the old oil. Obtain the correct quantity and type of gear oil recommended by the motor's manufacturer. A lube pump will also make your task easier. In addition, you will need new drain and vent screw gaskets as well as a large screwdriver.

Locate the oil drain screw and the oil vent screw on the lower unit. Your owner's manual has a complete diagram showing the locations of each. Place the container under the drain screw opening. Remove the upper or vent screw. Next remove the lower or drain screw to allow the gear oil to flow out into the waste container. Please dispose of the waste oil in the proper fashion.

Observe the appearance of the gear oil as it begins to flow out of the lower unit. The gear oil should look similar to new gear oil. If it appears dirty, too much time has elapsed since the last gear oil change. If the gear oil smells pungent, your lower unit is most likely in need of expert attention to determine the cause of this type of failure. If the gear oil looks milky, water is present in the lower unit. Seek expert attention immediately! If metal filings are observed, bring a large bag of money when you seek expert attention.

Refill the lower unit by attaching the lube pump to the bottom or drain screw opening. Continue filling the lower unit until lube oozes from the vent opening. Place one of the gaskets on the vent screw and insert the vent screw and tighten. Remove the lube pump from the drain opening and replace the drain screw with its new gasket into the drain opening and tighten.

Make sure to change the lower unit lube at the end of your boating season. This way you will insure that there is no water contamination to seize the gears and cause a very expensive repair in the spring.