Abstract: A shear liquid fan drive assembly for the radiator cooling system of an internal combustion engine of the type wherein a temperature responsive valve controls the degree of rotary coupling between the engine and a radiator cooling fan by controlling the quantity of shear liquid between a driving disc and a driven housing carrying the fan. The specific improvement relates to a bi-metal strip for the temperature controlled fluid coupling, the strip being so configured that its improper placement on the fluid coupling results in maximum fluid coupling and hence maximum cooling of the engine by the fan.