Abstract: A cooling system for marine engines for use in propelling a boat and wherein the propulsion system provides a flow of water to the engine for cooling and wherein the water is provided at a range of pressures including a high pressure, the cooling system including a pressure regulator for receiving the flow of water from the propulsion system and for providing this flow of water to the engine for cooling and with the pressure regulator providing the flow of water to the engine at a pressure substantially less than the high pressure from the propulsion system, a thermostat located to receive water from the engine and for regulating the flow of water from the engine in accordance with the temperature of the water from the engine, and the thermostat providing a minimum flow of water from the engine even when the water is at its coldest temperature.