Hydraulic system for a self-propelled work machine

The hydraulic system has a variable displacement pump (3) which is driven by an internal combustion engine (1). The supply volume of the variable displacement pump to multiple hydraulic circuits is varied by a regulating device (11) for driving a hydraulic motor (14) via a pressure line (7). The hydraulic motor has a cooling fan (16), where the performance of the cooling fan is temporarily reduced during a non-compensable pressure drop in the hydraulic system. The hydraulic motor and a working hydraulics (8) are jointly supplied with pressure medium from the variable displacement pump. An independent claim is included for a method for operating a hydrostatically driven cooling fan of a self-propelled agricultural working machine.