Change the Oil on an Outboard Lower Unit
The Lower unit on an outboard boat engine acts as a transmission would in a car, so it transfers the rotating power of the engine to the propeller by using different gears and ratios. It also allows you to put the boat on neutral, forward gear or reverse. The lower unit has oil in it that help preserve the gears from grinding and consuming. It is recommended to change the lower unit gear about every two years to properly maintain the gears inside. Here is the procedure on how to accomplish this task.
Steps
- Get your tools ready. For this project you will need a large flathead screwdriver, a large bucket to catch the old oil, some cleaning towels, new lower unit oil, a manual oil pump and two new sealing gaskets for the drain screws. All of these parts can be found on any marine store.
- Place the bucket underneath the outboard. You will need to catch the old oil in a bucket and after you are finished the oil has to be disposed correctly. Most auto-part stores will take used oil and recycle it with no cost to the consumer.
- Remove the upper oil level screw. Take the screw driver and remove the upper oil level screw by turning it counterclockwise.
- Remove the screw gasket from the drain hole. After you have removed the screw you need to remove the small gasket that is left behind on the oil level hole. It is recommended that this gasket is replaced with a new one to ensure proper sealing against the water when the motor is used.
- Remove the oil drain screw. Remove the oil drain screw using the flathead screwdriver by turning it counterclockwise. At this point make sure that the bucket is well placed underneath the drain hole to catch the oil and avoid any spills.
- Let the oil drain completely from the drain hole. Let the oil drain completely from the lower unit, wait a few minutes for the oil to drain slowly. Because gear oil is more viscous than engine oil it takes more time to pass through the seals.
- Inspect the old oil. At this point inspect the old oil, it shouldn't be creamy or white in color but rather dark and brown. If the oil looks creamy/white it is an indication that water has gotten into the lower unit and that the seals might be bad. If that is the case the lower unit should be rebuild or water might get into the gears and could cause catastrophic damage to the lower unit.
- Remove the drain plug gasket from the drain hole. This gasket should be removed and replaced with a new one to ensure proper sealing. At this time clean the oil drain area using a clean towel. The gasket is the same as in step 4
- Screw in the manual oil pump fitting to the lower drain hole.
- Screw in the fitting on the manual oil pump to the lower unit drain hole.
- Open the cap on the new oil bottle.
- Screw in the manual oil pump to the bottle neck.
- Start pumping the oil into the lower unit. Start pumping the oil into the lower unit by pushing on the manual pump. Take a 30 second brake after each pumping of the manual pump, this will ensure that the oil fills in slowly and doesn't damage any interior parts from excessive oil pressure. The lower unit will be filled when oil starts dripping from the top level hole. Stop pumping oil at this point.
- Screw in the oil level screw and gasket once oil starts to drip from the oil level hole. Once the oil reaches the top oil level hole it will start to drip, at this point the lower unit is filled with the required amount of oil. Install the gasket and screw by turning it clockwise using the flathead screwdriver.
- Remove the oil pump fitting and install the oil drain plug. Unscrew the oil pump fitting and quickly install the oil drain and gasket. Do this step as quickly as possible so large amounts of oil don't drain from the unit. Be careful when threading the oil plug not to strip the threads.
- Clean the screw locations and inspect for oil leaks. Clean the lower unit using a clean towel and inspect the screw locations for oil leaks. If no leaks are found the job is complete. If there are leaks from the two screw locations check the gaskets and the screw threads to make sure that they aren't damaged or stripped.
