How To Replace Gear Oil

Author: Stuart Buckingham   Date Posted:30 July 2020 

Blog How To Replace Gear OilWhether your outboard is 2 stroke or 4 stroke it will have a gearbox. The gearbox is the area of your outboard that the propeller is fitted to and, as the name suggests, a gearbox is where your outboards forward, neutral and reverse gears and bearings are located.

Keeping these gears and bearings in tip-top condition requires lubrication. Marine gear oil is what is used and should be replaced every season. It is a pretty simple task, provided you have the right tools and take the correct steps to do the job.

What you'll need:

  1. 1. Large flathead screwdriver
  2. 2. Gear oil pump
  3. 3. Sufficient gear oil to fill your gearbox
  4. 4. Drain screw washers
  5. 5. Container to catch the old waste oil (I suggest a large rectangular 4 to 10 litre container)
  6. 6. Rag

How to replace gear oil:

Step 1: Place your container under the lower drain washer

Step 2: Undo the bottom drain screw (ensure the washer is with the screw)

Step 3: Undo the top vent screw (ensure the washer is with the screw). The old oil will now drain properly

Step 4: Wait for the oil to completely drain. Ensure there is no water in the oil. A milky look generally indicates water intrusion

Step 5: Fit new drain screw washers to drain/vent screws

Step 6: Connect gear oil pump to bottom drain and pump new oil into gearbox until it comes out of the top vent

Step 7: With the pump still attached, quickly fit the top vent screw and washer. Ensure it is fitted firmly

Step 8: Carefully undo the gear oil pump from the bottom drain and swiftly fit the lower drain screw and washer

Step 9: Clean up with a rag

So, now you've finished the task of replacing your gear oil but I bet you are asking yourself "why did we fill the oil from the bottom and not the top?". The answer is simple, filling from the bottom forces any air inside the gearbox out and allows the gearbox to be full of gear oil and not air.

NOTE: When the top vent screw is fitted a 'vacuum' is created and this stops the gear oil rushing out. You may lose a small amount of oil when re-installing the bottom screw but this is pretty normal. Just ensure you fit the bottom screw relatively quickly and try not to cross-thread the screw when re-installing. My tip is to start the bottom plug first by hand and then use the screwdriver to finish off.

To shop for gear oil pumps and oil, click here.

Comments (1)

Very helpful Fergie box Royal exchange

By: on 1 April 2023
I think you covered the ground very well on explanation well-done David

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