This paper presents a workflow to analyze the lubrication and cooling performance inside an electric motor gearbox, under several operation conditions. The workflow starts by realizing a multiphase transient CFD analysis to estimate the oil wetted area and evaluate the heat transfer coefficient on solid parts. Then heat transfer coefficients are used in a steady-state thermal analysis to calculate operational temperatures. Various configurations are simulated to cover operational scenarios of the gearbox, such as different speeds, uphill or downhill and different weather conditions. Gearbox design involves multiple physics to be considered and proper lubrication to control internal temperatures is one important aspect. Using typical experimental test benches, it is very difficult to clearly visualize the oil behavior. CFD simulations allow to see how the lubricant behaves and to extract a tremendous amount of data to help the design. Ideal lubricant fluid level can be established and casing geometry with lubricant recovery channels can be optimized to better redirect fluid on hot surfaces (bearings). In this workflow, we are using CATIA Apps, in the Dassault Systèmes 3DExperience platform, to prepare a watertight CAD, vital for the CFD analysis. This step is often time-consuming, as CFD preprocessors are very sensitive about the CAD format for the solid tessellation phase. All solid parts, including the casing assembly, the shafts, the gears and the bearings are meshed during that phase. A methodology for gears and bearings modeling is presented. The mesh is exported as STL files, in order to accurately map the heat transfer coefficient at the node’s location without any extrapolation, for the thermal analysis. The CFD analysis is set up in XFlow, using the multiphase solver with Lattice-Boltzmann technology, allowing multiple rotating parts. GPU power is used to compute CFD analysis. Post-processing is done by creating animations, volumetric markers to visualize the wet areas of the gearbox mechanism and surface data integration to get quantitative values. The heat transfer coefficients are estimated everywhere and exported to be used as film conditions in the thermal steady-state analysis, with ABAQUS solver, using the same mesh. In the thermal model, heat generation from the bearings are defined from manufacturer data. Heat generated by gear friction, and contact thermal resistance are estimated. Heat transfer analysis allows evaluating the efficiency of the cooling down of the gearbox, highlighting the hot areas that need a better cooling. Data generated by this workflow allows the manufacturer to ensure gearbox reliability, preventing bearing or gear issues related to high internal temperatures. Predictive simulations are providing more information than a test bench and are becoming the most powerful ally to design sustainable and reliable.