Since inboard boat motors are basically automotive engines adapted to powering a boat, one could expect changing the oil in an inboard would be similar to changing the oil in a car or truck. It’s a similar process: remove the old oil and oil filter, then replace, but it’s different since it’s usually impossible to access the oil pan to remove the drain plug. Instead, the oil needs to be pumped out of the oil pan through the dipstick hole using a special dipstick oil pump.
Out With The Old
Remove the dipstick from the dipstick pipe on the boat’s motor.
Insert the suction tube of the oil pump down the dipstick pipe until you feel it touch the bottom of the oil pan.
Insert the discharge tube into a waste oil container.
Turn on the pump if your pump runs off its own pump motor, or attach the pump to an electric drill and turn on the drill if it’s a drill-powered model.
Listen to the sound of the pump motor or drill as the oil pumps out. When the last of the used oil is sucked out of the oil pan, the RPMs on the drill or motor will increase slightly. There may also be a “slurping” sound similar to draining the last drops of liquid from the bottom of a cup through a drinking straw.
Remove the suction tube from the dipstick pipe and replace the dipstick.
In With The New
Check the engine service manual to determine the oil capacity of the motor.
Remove the cap from the oil filler hole, insert a funnel and pour in the new oil. If the exact quantity needed is unknown, add approximately the amount of oil you pumped out, check the dipstick, then add more if needed and recheck the dipstick, continuing until the full level is reached.
Replace the oil filler cap, wipe up any drips with an old towel.
Remove and Replace the Oil Filter
Position an old towel in the bilge directly under the oil filter. This will catch and absorb the small amount of oil that will drain out of the fitting where the oil filter attaches to the engine.
Use an oil filter wrench to loosen the oil filter, then, by hand, unscrew it the rest of the way and remove.
Coat the rubber gasket on the top of the new filter with engine oil.
Thread the new filter onto the attachment threads until the rubber gasket just touches the mount, then tighten by hand an additional 3/4 of a turn.
Items you will need
- Dipstick oil pump
- Oil filter wrench
- Waste oil container
- Oil filter
- Old towel
- Some marine engines have a threaded collar near the top of the dipstick pipe to which an oil pump can attach. If yours has this you can eliminate the long suction tube and attach the oil pump directly to the dipstick pipe.
- Since the viscosity of engine oil thins as it gets warm, pumping the oil through a tube or dipstick pipe is easier when the engine is warm. If possible, run the engine for several minutes before starting to pump the oil out of the oil pan.
- If possible, run the engine for a few minutes after changing the oil, check for leaks around the oil filter, then use the dipstick to recheck the oil level.
- Over-tightening the oil filter can compress and distort the rubber gasket causing it to leak and will also make the filter difficult to remove during the next oil change.
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