A three-dimensional thermohydrodynamic model is developed to predict non-Newtonian lubricant behavior in slider bearings and channel flow. The generalized Reynolds equation is established using the concept of generalized Newtonian fluids (GNF) and the temperature field is determined with the energy equation. The chosen rheological models are the power-law, Bingham, and Hershel–Bulkley models. The last two models hold uniformly in yielded and unyielded regions using the approach proposed by Papanastasiou. The results present the evolution of the velocity, pressure, and thermal fields. The power loss, load capacity, and friction coefficient are analyzed. Comparisons are made with Newtonian lubricants and other recent non-Newtonian computational analyses.