Proper boat engine maintenance is necessary to keep one’s vessel running in the best condition possible. To maintain the engine, check and clean the boat engine’s spark plugs and replace the ones that are malfunctioning or defective. Check the engine’s oil level to ensure that it is adequate. The oil should be changed after 100 hours and the filter replaced once every three months. Inspect the battery’s charge as well as its terminals, and clean and grease them if they have buildup. As needed, spray an all-purpose oil on the electrical components of the engine to prevent rust. Look over the propeller and the engine belts for signs of excessive wear, replacing them as needed.