Abstract: A liquid cooling circulation system for power and working machines (especially internal combustion engines) contains an air-separating tank (17) in a by-pass vent line (14) which is arranged at the high point (5') of the radiator inflow (5). A fill inlet (19) with connecting openings (5" and 17') to the radiator inflow (5) and air-separating tank (17) have a closure cover (20) which closes off these connecting openings with respect to one another. Excess pressure, vacuum and vent valves (21 and 22) are contained in the closure cover 20 which controls a line connection (25) to an atmospheric, or to an excess pressure expansion tank (27). A highly effective venting function in conjunction with an engine operation at strong rotational speed changes exists, since the line connection (25) is opened at least at low cooling medium temperature by means of a temperature-controlled vent valve (22).