Exposure to water and other elements over time can cause the lubricant in your outboard’s lower drive unit to break down, increasing the chance of wear or damage to internal gears or causing difficulties when shifting. You can avoid these problems by changing the lower unit gear lubricant in your Mercury® outboard annually, or after every 100 hours of operation.

Replacing the lubricant removes contaminants, refreshes the lubricant’s protective additives and provides an opportunity to inspect the drive unit and lubricant for water intrusion. Quicksilver® SAE 90 High Performance Gear Lube (PN 858064Q01; 1-quart bottle) contains 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 Mercury and other leading brands.

For many boat owners, changing the gear lube is part of an annual service performed before winter or offseason storage. It’s a simple task for the do-it-yourself boater and can be accomplished easily with a few simple tools.

The step-by-step how-to videos below detail how to change gear lube in a variety of Mercury outboard models, most of which follow a similar procedure. Another helpful resource for the do-it-yourselfer is your Mercury operation and maintenance manual, which outlines the steps as well as the lubricant and capacity requirements for your specific drive unit. If you don’t have a manual, a copy may be downloaded or ordered directly from MercuryMarine.com or from a Mercury Authorized Dealer.

Pro Tips

Trim the outboard all the way down into a vertical position to check the oil level and when draining and filling the gearcase. The oil level rises and falls during drive operation; always check the level when the drive unit is cool and the engine is shut down. Periodically inspect lubricant for water to ensure the drive unit seals are not leaking. A milky appearance to the oil is an indication water may be leaking into the gearcase.

You’ll need to remove the propeller to access the drain and fill plugs for the lower unit on most Mercury outboard models. While the propeller is off, it’s also good time to check the hub kit for wear or damage as well as for any fishing line that might have worked its way onto the shaft, which can damage the prop shaft seal. Use Quicksilver 2-4-C Marine Grease or Quicksilver Extreme Grease to lubricate the prop shaft before replacing the propeller.

Essential Tools

Changing outboard gear lube in a Mercury outboard requires some basic hand tools, rags or paper towels, an oil catch pan and a container for the used oil. Having a Quicksilver prop wrench and a prop block handy will make removing the propeller easier. The Quicksilver gear lube pump kit includes a special fitting that threads into the lower unit and makes it easy to fill the drive with fresh lube. 

Completing this basic maintenance procedure as part of your regular annual maintenance routine is a simple way to keep your outboard performing at its peak for season after season of fun and reliable service on the water.