To keep heat out of the engine room, wet exhaust systems pass 800-degree exhaust gas through an inner pipe, and that inner pipe passes through a slightly larger outer pipe that carries seawater from the engine. Wet systems were popular from the 1970s through the mid-1990s, largely for looks, because those outer stainless-steel pipes can be polished to a mirror finish. But McLeod says a sparkling engine room isn’t worth the liability. “The pipe is double-walled starting right at the turbocharger,” McLeod says. “The day will come when that pipe will fail, and it will cost a lot of money in engine repairs.” In hours, or even a handful of minutes, leaking seawater can trickle back through the turbocharger, corroding it beyond repair, or into the engine’s cylinders, necessitating an overhaul.