Secret No. 2: Water on a plug doesn’t instantly mean a blown head gasket or cracked block.
Some mechanics, when finding water on a spark-plug electrode, will jump the gun and replace the head gasket or give the engine a complete top-end rebuild. It’s a huge expense. The cause, however, may be as simple as water in the fuel. Ask your mechanic about the integrity of what’s in the tank. Our experts have also seen faulty or inadequate gaskets on hatches that let rain leak directly into the flame arrester and accumulate in the engine. Loose exhaust bellows can allow water to backflow into the engine if there’s a highspeed shutdown, like when you drop a skier or back down on a fish, and an overloaded boat can lower the exhaust elbow height enough to allow water to enter.