This paper studies the sensitivity of the thermal behavior of a high power density electric motor to some parameters. The machine is conceived for aeronautical application. It is of Permanent Magnet Synchronous type totally enclosed, configured with a double cooling system around the stator and in the shaft. A Lumped Parameter Thermal Model of the motor is primarily elaborated to explore hot spot points. Then, the thermal parameters, related to the heat evacuation from the critical zones, are investigated. Windings' thermal conductivity as well as laminations' one appear to influence the most the hottest regions of the machine.