How to Change Lower Unit Gear Lube

The lower unit gear lubricant in most outboard motors and sterndrives should be changed annually, or every 100 hours. For many boat owners changing the gear lube is part of an annual service performed before winter or off-season lay-up, along with an engine oil-and-filter change for four-stroke outboards and sterndrives. Changing the lubricant is a pretty easy task for the do-it-yourself boat owner.

In this how-to video, Scott Glorvigen of Wired2Fish and the Lund Boats Pro Staff demonstrates how to change the gearcase lube in a Mercury Pro Kicker outboard, and the procedure is the same for most outboards and sterndrives. Check your owner’s manual for instructions specific to your motor or drive.

Changing gearcase lube is important for two main reasons. First, like any lubricant, gearcase lube wears out with use as its additives break down and it holds fine metal particles in suspension. Second, draining the lube can reveal the presence of water in the gearcase – if the lube looks cloudy or milky it’s likely water is entering the case, and that water can destroy the gears and bearings in short order. If left in the case during cold weather, water in the gearcase can freeze and expand, which could crack the aluminum case. If you observe water in the gear lube, the likely cause is a failed propshaft seal, which should be replaced by a professional technician.

Quicksilver offers three gear lube products which provide outstanding performance in any outboard or sterndrive gearcase. Each has a specialized marine additive package that provides protection against excessive wear even in the presence of water, prevents corrosion and pitting, and helps extend gear life. Quicksilver Premium Gear Lube is recommended for use in lower units of outboards below 75 horsepower. Quicksilver Extreme Performance Gear Lube is designed to deliver maximum performance for outboard and sterndrive racing applications. Consult your engine owner’s manual for gear lube specifications for your outboard or sterndrive.