Heat transfer in a turbocharger plays a crucial role in the optimization of turbocharger-engine matching process. Due to high temperature gradients between the hot exhaust gas compared to the compressor as well as the environment, it is well-known, that the heat loss from a turbocharger turbine is significant. Investigations of turbocharger performance are commonly done by quantifying the performance parameters under adiabatic conditions, following the paradigm of the first law of thermodynamics, based on the energy balance method. It turns out that an adiabatic assumption and the energy balance method is insufficient to provide a deep understanding about the aerothermodynamic effects on the turbine performance due to heat transfer. Based on the current state-of-the-art, this study aims to improve the characterization methods for passenger car turbocharger turbines, considering the impacts of heat transfer. Firstly, the turbocharger is measured on a hot gas test bench. Based on this experimental data, the turbine heat transfer is being quantified through implementing a new innovative power-based approach. Consequently, a heat loss free turbine performance map can be derived. Secondly, a CFD analysis is performed on selected operating points, taking turbine housing temperature measurements as boundary conditions. CFD results are verified and validated by using the experimental data, both at adiabatic and diabatic test conditions. Finally, a flow exergy-based method is being applied to the predicted 3D flow field from the CFD simulation. This approach allows to identify and quantify the aerothermodynamic impacts of heat transfer on the turbine performance for cases with and without heat loss, considering both first and second laws of thermodynamics. This study aims to enhance our understanding of the underlying thermo-fluid physics in a turbocharger turbine associated with heat loss. It will also demonstrate the potential of the application of flow exergy method to 3D CFD data, rather than limited to 1D adiabatic models in current engine research and development.