in grooves 52 and 53 a fluid chamber 54 is defined about the spacing between the input and output members the chamber is closed by wall 55 extending from flange 41b to flange 45c of the input member the wall 55 has a plurality of radiating or cooling fins 56 wall 55 has a solid connection to the outer flange 41a but extends closely adjacent the interior periphery of the inner flange 45c the spacing therebetween being sealed by an element 57 the driving connection from the output member 41 to the blower impeller is provided by way of a wheel or flange 58 coupled at 59 to the output member the wheel 58 has an outer cylindrical surface 60 contoured to receive a pulley belt 61 thereon which in turn connects with the impeller the input member 45 is rotatably journalled on the oneway clutch 27 which in turn is mounted about the accessory shaft 32a the overrunning clutch 27 may be of a conventional construction utilizing a plurality of sprags 62 and bearings 64 retained within a cage 63 so that relative rotation between the accessory shaft acting as the inner race and the coupling input member 45 acting as the outer race is permitted in one direction and not the other the sprags are tiltable for making a positive drive or withdrawing positive drive therebetween the clutch 27 permits overrunning of the viscous shear coupling with respect to the output shaft 20 the positioning of the viscous shear coupling unit on the accessory shaft with the accessory shaft extending therethrough permits all other power take off.