Quick Maintenance: Changing Outboard Lower Unit Oil

Changing your outboard’s engine oil is Maintenance 101, but it’s easy to overlook another equally important oil to your motor’s health: the gearcase lube.

Regularly changing the gearcase lube (aka lower unit oil) ensures the internal components are well lubricated at all times.

Without oil in the gearcase, the various gears, bearings and other moving parts quickly wear to the point of failure. Most outboard manufacturers recommend the lower unit oil be replaced at least once every 100 hours of use or once per year. Consult your outboard’s owner’s manual to determine how frequently the gearcase lube should be changed in your particular make and model.

Changing gearcase lube is a simple maintenance task that can be taken care of in a matter of minutes. All you have to do is remove the drain/fill screw and vent screw from the lower unit, then let the old oil drain out and pump new oil in until it overflows from the vent hole. Next, reinstall the vent and drain/fill screws and the job’s done.

Benefits of Changing Lower Unit Oil

Gear lube gets contaminated with thousands of tiny metal particles from all the moving parts within the lower unit. These contaminants increase gear wear, and replacing the lube removes the contaminants. Old lower unit oil also loses its ability to absorb heat effectively. Gearcase oil absorbs frictional heat from the moving parts and dissipates it, thereby cooling the lower unit. 

Draining old lower unit oil tells you whether a seal is leaking in the gearcase. If the oil is milky, it’s an indication that water is mixing with the oil, which means the seals need replacing.

By helping to lubricate and cool the internal components, fresh gearcase oil helps maximize the life of the lower unit. Whenever you’re ready to change out the gearcase lube in your outboard, watch one of our videos above to see how it’s done.