Today’s marine engines are high-tech wonders. Flush them and change the oil at regular intervals, and you should expect hundreds of hours of faithful service. Yet we still often hear casual boaters wondering why a boat can’t achieve the fuel efficiency and longevity of the truck that tows it, especially since they share the same engine block. Here’s why.
An automotive engine kicks down to a lower rpm at top speeds. In contrast, a marine engine’s sustained speed only increases with sustained rpm. Basically, a truck motor has four to six gears, and a marine motor has one. It only makes matters worse when a boat engine isn’t properly broken in.
Frequency of Use
A car engine has an advantage in that it gets run every day, and engineers say hours are good. Think of it in terms of physics. Things in motion stay in motion. An object at rest tends to rust — from the inside out.
A car typically runs on a dry road, has plenty of ventilation and is better regulated in temperature thanks to closed cooling systems (like a radiator). In contrast, a boat is always operating in a moist, corrosive environment and is typically cooled by the surrounding waters — and then there’s the shakedown from high seas. The motor essentially takes a steam bath, if not a beating, every time out.
Bottom line: Marine mechanics tell me most of the problems they see are primarily due to user neglect. These include the use of cheap lubricants, improper break-in, overpropping, etc. The engine doesn’t suddenly decide it’s tired and done. Something led up to it.