A viscous fluid clutch employing a magnetic field selectively actuatable by a heat sensing device to operate a valve arm to seal an inlet passage fluidly communicating an operating chamber with a storage chamber. The clutch includes a clutch and a housing member rotatably disposed relative to one another. Each member has a shear surface. The surfaces define therebetween the operating chamber. The storage chamber is located in the housing member and is in fluid communication with the operating chamber via a discharge passage and the inlet passage. Pump means in the operating chamber displace fluid through the discharge passage from the operating chamber to the storage chamber. The inlet passage directs fluid from the storage to the operating chamber. A movable valve arm selectively seals the inlet passage. The valve arm is moved via a solenoid action in response to actuation of the magnetic field. Fluid is disposed within the clutch and is used, when located in the operating chamber, to rotate the housing members in response to rotation of the clutch member. When the fluid is displaced from the operating to the storage chamber, rotation of the housing member is reduced.
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