A model is developed to investigate the effect of radial grooves and waffle-shape grooves on the performance of a wet clutch. Three-dimensional formulation of the governing equations, boundary conditions, and numerical solution scheme are presented for modeling the thermal aspects of the engagement process in a wet clutch. The thermal model includes full consideration of the viscous heat dissipation in the fluid as well as heat transfer into the separator, the friction material, and the core disk. The convective terms in the energy equations for the oil as well as the heat conduction equations in the bounding solids are properly formulated to determine the temperature fields corresponding to the domains between grooves. Roughness, centrifugal force, deformability, and permeability of the friction material with grooves are taken into account. The effects of groove geometry such as groove depth, grooved area, and number of grooves on the engagement characteristic of a wet clutch are investigated. It is also shown that the thermal effects in a wet clutch influence the engagement time and the torque response and should be included in the analytical studies.