How to Change Outboard Gearbox Oil

Changing the oil in your outboard gearbox is a straightforward and crucial maintenance task. Neglecting this can lead to accelerated wear and tear on the internal components of your costly gearbox.

If you notice dark or black oil with a burnt smell, it indicates that your oil has become old and has gone too long without a change. The recommended interval is once a year or every 100 hours, whichever comes first. However, consult your motor's owner's manual for manufacturer-specific recommendations.

On the other hand, if you see white or milky-looking oil, it signifies the presence of water in your gearbox, often caused by damaged seals. If you suspect water contamination, it's essential to have your gearbox undergo pressure and vacuum testing to identify the source of the leak.

Common causes of leaking seals include:

• Fishing line entangled behind the propeller, leading to damage to the propeller shaft seals.
• Damaged or missing drain screw washers.
• Stuck or worn shift rod O-rings/seals.
• Upper driveshaft seals, typically located under the water pump.
• Only a pressure and vacuum test can pinpoint the actual cause of the seal issue. We recommend having a local service technician perform these repairs.

Inspect the drain screw magnets:

Most outboard drain screws come equipped with small magnets designed to capture any metal particles in the oil. While some metal sludge is normal, the presence of chunks or metal pieces that you can feel suggests internal gearbox damage. In such cases, it's advisable to schedule an inspection with a technician. If you find metal sludge on your magnet, it may indicate that you are shifting gears too slowly, potentially causing damage to your gearbox's gears and clutch dog.

Here are the steps to change the oil:

1. Begin by draining the gearbox oil, starting with the lower drain screw, followed by the top drain screw.
2. Allow the oil to drain completely.
3. Replace the drain screw washers with new ones.
4. Use a pump to fill the gearbox with oil through the bottom hole until it emerges from the top vent hole.
5. Allow the oil to settle for a few minutes to let any air bubbles escape, then add more oil to the gearbox.
6. Install the top vent plug with the new washer and tighten it securely.
7. Remove the pump from the bottom fill hole, and reinstall the drain screw plug with a new washer. Ensure you've removed the old washer or seal, and double-check for any lingering washers from previous oil changes.

Click here to see our range of outboard gearbox oil lubricants and pumps.