Mercury Tracker 25 Gearcase Oil Change

When was the last time you changed your outboard’s gearcase lube? Manufacturers recommend the lower unit oil of an outboard be changed after every 100 hours of use or once a year. 

Watch the video above and follow the steps below to change the gearcase oil in a Mercury Tracker 25 outboard.

NOTE: The steps to change the lower unit oil on a Mercury Tracker 25 are the same or similar for almost all outboard makes and models. 

Tools and Parts – Mercury Tracker 25 Gearcase Oil Change

• Flathead screwdriver
• Contact/brake cleaner
• Drain pan
• Mercury gear lube pump
• Mercury gear lube

PRO TIP: The OEM Mercury brand gear lube pump comes with the correct attachment for Mercury outboards, so you won’t have to buy an additional adapter.

How to Change Mercury Tracker 25 Gearcase Oil

Step 1. Remove the vent screw and washer from the top right side of the lower unit.

Step 2. Position a drain pan under the lower unit, and remove the drain/fill screw and washer from the bottom right side of the lower unit. Let the gearcase oil drain out.

Step 3. Inspect the vent screw washer and the drain/fill screw washer for wear, and replace them if necessary. 

PRO TIP: To ensure there are no oil leaks, the washers should be replaced every couple of lower unit oil changes, regardless of their condition. 

Step 4. Attach a Mercury gear lube pump to a quart bottle of Mercury SAE90 gear lube, then attach the other end of the pump to the drain/fill hole in the lower unit.

Step 5. Slowly pump the new gear lube into the lower unit until it starts to flow out from the vent hole.

Step 6. Reinstall the vent screw and washer into the lower unit.

Step 7. Remove the gear lube pump, and quickly reinstall the drain/fill screw and washer into the lower unit.

Step 8. Clean away any spilled oil from the lower unit using contact/brake cleaner and you’re done. 

NOTE: Polluting water with even the smallest oil spill is a federal crime that carries a hefty fine, so make sure the gearcase is totally clean after replacing the lower unit oil.