This paper presents analytical model and simulation results of auxiliary cooling system of a hybrid electric vehicle consisting of drive train motor/generator set and its power-electronics. The cooling requirement of auxiliary circuit is different from that of the conventional engine cooling system due to different temperature levels of power electronics and engine cooling system. This, therefore, necessitates two separate cooling loops to meet the requirements of the individual systems.Steady-state analysis is done using standard simulation tool for auxiliary cooling system to predict the temperature and pressure levels at different locations. Cooling layout is chosen for flow and thermal requirements of the individual systems. Basic analytical model is also created to validate the simulation results.Detailed transient analysis of the cooling circuit is done, for a given drive cycle, of the hybrid electric vehicle. Two radiators placed at different locations are used for the auxiliary cooling system to reduce the peak temperature of electric drive train aggregates. Auxiliary radiator fans are switched ON and OFF based on optimally selected “High” and “Low” threshold values of motor inlet coolant temperature. Pump flow rate is varied to reduce power consumption at lower ambient temperature.