The increasing importance of electric mobility results into the need for optimizing all power train components to further reduce the energy consumption of the vehicle. The aim of this study is to predict the thermal behavior and the pressure losses in water jackets of electric machines by use of CFD.The heat loss of electric machines in passenger cars is sufficient to let its components reach critical temperatures. For this reason, the optimization of heat dissipation plays an important role. The goal of efficient heat dissipation is a high heat transfer coefficient. At the same time, the pressure loss should be low in order to reduce the required power of the pump. Flow simulations can help to evaluate different water jacket concepts in an early stage of development.In this work, the validation of flow simulations in water jackets is based on measurements of a simplified geometry with constant boundary conditions. Afterwards, a coupled flow simulation of Exa PowerFLOW® and Exa PowerTHERM® is set up with the boundary conditions adopted from the measurements. A comparison of the results shows good correlation for the investigated flow rates, inlet coolant temperatures and wall temperatures. The deviation of the pressure losses between measurement and simulation are close to the measurement accuracy.With these results it is possible to develop and optimize water jackets based on a digital development process. Additionally, this enables to obtain the characteristic map for heat transfer coefficients and pressure losses of digital prototypes for cooling system simulations in the early development phase.