Abstract: A cooling installation for liquid-cooled internal combustion engines, especially for water crafts having a combined fresh-water/sea-water cooling system of the internal combustion engine, with a housing that includes a liquid heat-exchanger for the engine cooling medium and an external cooling medium, a by-pass channel for the engine cooling medium in parallel to the heat-exchanger, a mixing chamber for the cooled and non-cooled portion of the engine cooling medium and a thermostat for the temperature-dependent proportional through-flow control of the engine cooling medium through the heat-exchanger and through the by-pass channel; the mixing chamber is arranged at a distance from the outlet side of the heat-exchanger while the thermostat is arranged in the mixing chamber and alternately controls a respective inlet opening leading into the mixing chamber; a closure cover which is removably secured externally at the housing is arranged opposite an inlet opening of the mixing chamber and closes off an installat