Abstract: A viscous fan clutch is typically employed in a fan drive mechanism within a truck or automobile. A shaft, driven by the engine, rotates a clutch member within the fan drive. The clutch member is arranged for fluid engagement with a body member for the transmission of torque thereto when the fluid is disposed in an operating chamber defined by complimentary shear surfaces in the clutch and body members. During relative rotation between the two members, fluid is pumped through a radially disposed standpipe to a point within a fluid storage chamber near the axis of rotation to prevent bleed back of the fluid through the pump at times when the pump pressure is relatively low.