Abstract: A flushing system provides a pair of check valves that are used in combination with each other. One of the check valve is attached to a hose located between the circulating pump and the thermostat housing of the engine. The other check valve is attached to a hose through which fresh water is provided. Both check valves prevent flow of water through them unless they are associated together in locking attachment. The check valve attached to the circulating pump hose of the engine directs a stream of water from the hose toward the circulating pump so that the water can then flow through the circulating pump, the engine block, the heads, the intake manifold, and the exhaust system of the engine to remove seawater residue from the internal passages and surfaces of the engine. It is not required that the engine be operated during the flushing operation.

Abstract: The engine (11) of a stern drive (10) is provided with a vacuum relief valve (28) to relieve any vacuum which may occur in the exhaust manifold (16), thus preventing water from entering the engine through the exhaust system. The relief valve (28) is connected to allow one-way flow from the intake manifold (15) to the exhaust system, thus providing an essentially closed system.