An increase of the e-motor operating temperature above critical levels reduces especially the life expectancy of the insulation material, which potentially results in the destruction of the motor. High temperatures also increase winding resistance. Cooling decreases the resistance and electric losses respectively. Lower electric losses reduce the amount of (expensive) copper required to achieve the targeted machine performance. The presentation shows how CFD simulation helps to determine the thermal load of electric motors and how to develop the optimum cooling system for maximum performance and life time.