Fuel economy is one of the factors that drives the automobile sector today, and the demand for fuel efficient vehicles continues to increase by the day. Power loss in the vehicle driveline directly affects the fuel economy and must be reduced to achieve maximum fuel economy. Churning causes power loss and needs to be estimated at the design stage to arrive at the most fuel-efficient design. Using the commercial CFD tool ANSYS Fluent, as explained below, is one such way to estimate it.Using this new method, and the steps within, permits the estimation of churning/splash losses for the complete manual transmission gear box. In the first step, CFD models are prepared to estimate the splash loss and windage loss for single gear wheel and validated against the measurement data. In the second step, a CFD model is created to estimate the splash losses for a gear pair which includes intermeshing power loss due to oil squeezing between the gear teeth, as validated by the published data. In the third step, a parametric study is done for a gear pair to find out the percentage of intermeshing losses for different operating conditions such as rotational speed, temperature and oil level. Finally, in the fourth step, a CFD method is proposed to estimate the splash losses for the complete Manual Transmission (MT) gear box.Considering the static condition of gear box, splash loss is estimated for the gears dipped in the oil and windage power loss is estimated for the gears away from oil. To estimate the splash loss of gear pair, the individual contributions of each gear are then summed up and the percentage of intermeshing losses are added to the sum value. Splash losses for all gear pairs are added to determine the splash loss for complete gear box.