How to Change MerCruiser Gear Lube

The lower unit gear lubricant in a Mercury® MerCruiser® sterndrive should be changed annually, or after every 100 hours. Replacing the lubricant removes diminished additives and contaminants and provides an opportunity to inspect the lubricant for water. For many boat owners, changing the gear lube is part of an annual service performed before winter or offseason lay-up, along with an engine oil-and-filter change.

Changing the lubricant with quality SAE 90 Quicksilver® High Performance Gear Lube is not a challenging task for the do-it-yourself boat owner. This video hosted by Scott Glorvigen of Wired2Fish demonstrates the process of changing gear lube in the popular MerCruiser Alpha One® Gen II drive mated to a MerCruiser 4.3L engine. The procedure will be similar for other MerCruiser drive/engine combinations. Your MerCruiser owner’s manual will outline the steps for your particular drive. Note that the shape and location of the gear lube monitor may be different than that shown in this video. If you don’t have an owner’s manual, a copy may be downloaded or ordered directly from MercuryMarine.com or from a Mercury Authorized Dealer.

Pro Tip: The oil level in the gear lube monitor will rise and fall during drive operation; always check oil level when the drive is cool and the engine is shut down. Periodically inspect lubricant in the monitor for water to ensure that drive unit seals are not leaking.

Essential Tools

Changing sterndrive gear lube requires some basic hand tools, rags or paper towels, an oil catch pan and a container for the used oil. Quicksilver High Performance Gear Lube has a specialized marine additive package that outperforms automotive gear oil in marine gearcase applications. It is formulated to meet or exceed manufacturer specifications for use in engines from MerCruiser and other leading brands. The Quicksilver gear lube pump kit includes a special fitting that threads into the MerCruiser drive and makes it easy to fill the drive with fresh lube. Quicksilver drain and fill screw seals are a direct replacement for seals that may be worn, damaged or lost.

Always dispose of waste oil properly. 

Mercury, MerCruiser, Quicksilver and Alpha One are registered trademarks of Brunswick Corporation.