Abstract: An apparatus for regulating the coolant circuit for an internal combustion engine is equipped with a radiator and a heating system heat exchanger, a water pump, and a thermostat valve which makes possible two circuits in the warmup phase of the engine or at low engine temperatures, one circuit being provided for cooling the engine via a bypass line, and a second circuit being provided to the heating system heat exchanger via a heating system line. A differential pressure valve, regulated as a function of engine speed, is arranged in the bypass line, the bypass line being blocked, and all of the coolant being passed through the heating system line, in the warmup phase or in the phase with a low engine temperature when the speed of the engine is low; and the differential pressure valve opening and uncovering the bypass line at higher engine speeds, a quantitative distribution of the coolant occurring via the bypass line and the heating system line as a function of the design of the differential pressure valve.