The invention relates to a cooling circuit of an internal combustion engine of motor vehicles, comprising a main cooling circuit that encompasses a section located upstream of the radiator, a main radiator, a radiator return path, a coolant pump, a main thermostat, and a bypass or short circuit which is disposed between the main thermostat and the coolant pump. Said cooling circuit further comprises a low-temperature circuit encompassing a low-temperature radiator, a low-temperature radiator return path, a valve unit, and an additional heat exchanger.