Summary: Neglecting lower unit maintenance on your outboard can lead to unnecessary damage and costly repairs, and worst yet down time right in the middle of your duck hunting season. Here’s how you can change the oil in your outboards lower unit and save $60 from taking your outboard to a boat shop.
Changing the oil in the lower unit is very simple, and there’s no reason you can’t do it your self and save some money. The only tools required are a flat-head screwdriver and an oil drain pan. A bunch of paper towels will also come in handy. The oil you want is API GL5 SAE 80 or 90 weight and is available at most Wal-Marts or your local marine dealer. The job should only take 10-20 minutes. This oil is often referred to as “Hi Vis”.
Step 1: First, be sure your outboard is in a vertical and upright position. Place an oil drain pan beneath the outboard. Now locate and identify the upper and lower Vent & Drain Screws on your outboard on shown in our photo.
Step 2: Remove the BOTTOM drain screw first (not the top). Some oil will begin to trickle out so be sure your oil drain pan is positioned correctly to catch the draining oil. If water starts coming out or the oil is really milky in color you have a problem and need to bring your motor to the shop.
Step 3: Next, remove the TOP vent screw. This will release the vacuum that exists and allow the oil to drain freely from the lower unit.
Step 4: Let all of the oil drain completely from the lower unit (this will take about 5-10 minutes). Very little water should drain out, less than a teaspoon. The oil should also not appear to be milky. Excessive water in the lower unit could cause it to crack in freezing temperatures.
Step 5: Once all the oil has completely drained out it is time to refill the lower unit. There are several types of apparatuses available ranging from squeeze bottles to tubes. The most popular and what we have always used is the squeeze bottle type. To refill the lower unit, insert the bottle/tube into the BOTTOM drain hole. Then slowly squeeze the bottle to force the oil into the lower unit.
Step 6: Continue adding oil until the lubricant is flowing freely from the top hole and is free from air bubbles.
Step 7: Keep the bottle/tube in the bottom hole (or plug the hole with your finger) and re-install the TOP plug. This will create a slight vacuum that will minimize the oil loss while you reinstall the bottom plug.
Step 8: QUICKLY remove the bottle (or your finger) from the bottom hole and install the drain plug. It is important to do this as quickly as possible to minimize the amount of oil loss. Even though there is a slight vacuum, there will still be some loss of oil. Do not be concerned about losing some oil, however, if you lose an excessive amount of oil you will need to go back and add additional oil. Tighten both the lower and upper drain screws and wipe off any oil on your lower unit.
Comments: To check your oil level, remove the top oil plug, insert a small piece of wire straight into the top hole approximately 1 inch and withdraw the wire. If oil is on the wire the oil level is correct, if not the unit must be refilled to the correct level.