Changing your gear oil on your outboard engine is one of the most important maintenance procedures you can do and it’s extremely easy with minimal cost. I usually change my gear oil between 80-100 hours of use and never going over a 100 hours.
You will only need a few tools and a couple of parts to complete the job.
1) A large regular screwdriver
2) Oil drain pan
3) Gear oil pump with lower unit adapter
4) Gear oil
5) New Gear Case screw washers (very important)
To start simple loosen the bottom screw on the lower unit and make sure the oil pan is underneath before loosening the top screw. Once you loosen and remove the top screw the oil will drain very quickly into the pan. I usually wait about 10-15 minutes to allow all the oil to drain before attaching the gear oil pump and adapter. You can pick-up a gear oil pump from any marina, west marine, marine hardware store and even some walmarts carry them. The item is relatively inexpensive $10-15 and will last you many years. The Gear oil you can pick up at the same stores in most cases. The screw washers you will need to replace you can get from your local marine dealer that services your particular engine. This is very important do not reuse your old washers by doing so can allow water to enter your lower unit and cause major damage. These washer only cost a dollar. I buy additional ones so I always have them on hand for the next oil change.
Once you attached the gear oil pump and adapter to the lower screw hole begin pumping the oil in until it starts flowing out of the top hole. Once the oil is flowing out of the top hole smoothly with no air bubbles place the top screw in finger tight and remove the pump adapter then place the bottom screw in. Now that both screws are in place, fully tighten them. You’ve just changed your gear oil. Pretty easy and you’ve saved yourself a few dollars by not having to go the marina.
For a more detailed explanation please watch video here: How to change you lower gear Oil.