US Patent 7503819 Closed cooling system for a marine engine

A cooling system for a marine propulsion device provides a closed portion of the cooling system which recirculates coolant through the engine block and cylinder head, the exhaust manifold, and the exhaust elbow. It provides a pressure relief cap connected to the exhaust elbow and a low velocity portion of the coolant jacket of the exhaust elbow to facilitate the release of gas and coolant when pressures exceed a preselected magnitude.