Transient heat transfer measurements are performed on an additively manufactured real-scale cooling configuration with ribs on one side. A test rig is presented that operates at elevated pressure and provides a sudden temperature step in the fluid to heat the model walls. It enables the establishment of application-relevant flow conditions under which the local heat transfer characteristics are investigated while the manufacturing-related wall roughness can be preserved. The small dimensions prevent a direct temperature measurement in the cooling channels and a direct observation of the heat transfer surface is not possible. Thus, the fluid temperature is measured upstream and downstream of the model and the temperature response on the outer surface is measured by infrared thermography. Analytical modeling of the fluid temperature and a numerical method for calculating the 3D temperature propagation inside the model wall enable the determination of local heat transfer coefficients on the inner heat transfer surface. The crucial temperature data filtering and its effect on the results is described. A sensitivity analysis is performed to determine the best-suited evaluation times locally. The results of the developed method are compared to results from former measurements applying a well-established evaluation method on an up-scaled model with similar geometry.