Viscous couplings have started to find widespread use in automobiles in recent years and it is important to have a good understanding of their torque transmission characteristics. This paper presents the results of transmitted torque calculations, which took into account temperature changes in viscous coupling components, and the findings of experiments carried out to verify the calculations. The results obtained made it possible to predict quantitatively the degree of influence that various factors have on the torque transmission performance of a viscous coupling.In addition, a mechanism is proposed for explaining the occurrence of the torque hump phenomenon. A calculation model was developed on the basis of this mechanism and used to calculate torque hump characteristics and the interval from the onset of viscous coupling operation to the occurrence of a hump. The calculated results are shown to correlate well with experimental data.