More stringent Federal emission regulations and fuel economy requirements have driven the automotive industry toward more efficient vehicle thermal management systems to best utilize the heat produced from burning fuel and improve driveline efficiency. The greatest part of the effort is directed toward the hybridization of automotive transmission systems. The efficiency and durability of hybrid powertrain depends on the heat generation in electric motors and their interactions among each other, ambient condition, the cooling system and the transmission component configuration. These increase the complexity of motor temperature prediction as well as the computational cost of running a conjugate heat-transfer based CFD analysis. In this paper, 1-D physics based thermal model is developed which allows rapid and accurate component-wise temperature estimation of the electric motor as well as transmission lubricant temperature during both steady-state and transient driving cycles. The complex and combined effect of heat convection, conduction and radiation have been considered while developing the energy conservation equations. The model represents a useful tool to design and analysis of a cooling system for the electric motors of the PHEV transmission systems and thus to develop more sophisticated thermal control system strategies with variable coolant flow control devices. For a robust analysis the Simulink version of the model was integrated with Flowmaster based engine cooling network. The critical temperature prediction from the proposed model exhibited good agreement with real-vehicle based test data under different drive cycles.