For being fairly straightforward machines, outboard motors have a lot of parts—and that’s especially true for lower unit and the drive system. Because there are a handful of moving parts, all of which create friction when they turn against one another, and because a decent amount of these products are usually underwater propelling the boat through the water, they rely heavily on seals and o-rings. These outboard motor seals and o-rings serve a variety of purposes on the engine. First, they help create air- and watertight compartments that keep oil and grease in the parts of the motor where they belong, and keep water out of the compartments where it doesn’t belong. Similarly, o-rings allow for a tighter seal in particularly high pressure environments which is important when you’re keeping oil, water, and air away from one another. Outboard boat motors rely on very precise mixtures of air and fuel to properly run, and misplaced water can create issues for an outboard—even if it’s down the line. Because these seals and o-rings are put under great pressure and often have to endure high temperatures, they sometimes wear out. Or, if they’re not used regularly (like when a boat is sitting in dry dock), they can dry out and get brittle. This causes the seals and o-rings to crumble and fall apart when they’re put back into use. Use our Marine Engine Parts Selector Tool to find the right engine parts for your boat.