Abstract: In a cooling circuit for internal combustion engines which includes a cooling jacket of the engine, a coolant pump, a radiator, a mixing thermostat, and an expansion tank, an excess-pressure valve is connected in the area between the cooling jacket and the radiator and a vacuum valve is connected in the area between the radiator valve of the mixing thermostat and the suction side of the coolant pump; both valves are connected with the coolant reservoir in the expansion tank which in communication with the atmosphere, is without excess pressure; high excess pressure values as well as low vacuum values in the cooling circuit are precluded thereby; a vent valve provides for an especially effective venting of the cooling circuit into the expansion tank in cooperation with the sucking back of coolant into the cooling circuit by means of the vacuum valve.