Patent ID: 7392769

Claim:
A cooling system for a combustion engine having a cooling passage system in an engine block, said cooling system comprising: a main cooler which is arranged in a cycle with the cooling passage system of the combustion engine, a pump and a first thermostat in said cycle, wherein said main cooler, said pump and said first thermostat are connected in series between an inlet of the cooling passage system and an outlet of the cooling passage system to define said cycle, a heat exchanger which is connected to the pump through a bypass passage, said bypass passage being outside said cycle, and a second thermostat in the bypass passage, wherein said heat exchanger, said pump and said second thermostat are connected in series between the inlet and outlet of the cooling passage system, a second opening temperature of a thermostat valve of the second thermostat is lower than a first opening temperature of a thermostat valve of the first thermostat, the thermostats being connected, by an interconnection passage, in series between the inlet and outlet of the cooling passage system, wherein when the thermostat valves are closed at a cooling fluid temperature below the second opening temperature, a minimum amount of cooling fluid flows through the cooling passage system (i) through the heat exchanger and (ii) without any flow of the cooling fluid through the main cooler, when the thermostat valve of the second thermostat is opened and the thermostat valve of the first thermostat remains closed at a cooling fluid temperature between the first and second opening temperatures, a larger amount of cooling fluid flows through the cooling passage system (i) via both the heat exchanger and the interconnection passage between the first and second thermostats, and (ii) without any flow of the cooling fluid though the main cooler, at a cooling fluid temperature at or above the first opening temperature, the thermostat valve of the first thermostat is opened to allow the cooling fluid to flow though the cooling passage system via the first thermostat and the main cooler.