A hydraulically controlled fan drive system is provided including a housing containing a hydraulic fluid, a pulley connected to the housing a fan shaft rotatably mounted to the housing by a hydraulically actuated clutch, a piston mounted within a piston housing for actuating the clutch, a pitot tube for delivering pressurized hydraulic fluid from the housing to the piston housing, a valve for controlling the fluid pressure within the piston housing, a shaft rotationally supporting the housing having passages extending through the pulley, a base connected with the shaft connecting the shaft with a structure, the base having coolant inlet and outlet, and an oil cooler connected with the base on a side of said base generally axially opposite of the pulley.