In the digital prototype development process of a new Mercedes-Benz, thermal protection is an important task that has to be fulfilled. In the early stages of development, numerical methods are used to detect thermal hotspots in order to protect temperature sensitive parts. These methods involve transient full Vehicle Thermal Management (VTM) simulations to predict dynamic vehicle heat-up during critical load cases. In order to simulate thermal control mechanisms, a coupled 1D to 3D thermal vehicle model is built in which the coolant and oil circuit of the engine, as well as the exhaust flow are captured in detail. When performing a transient 3D VTM analysis, the conduction and radiation phenomena are simulated using a transient structure model while the convective phenomena are co-simulated in a steady state fluid model. Both models are brought to interaction at predetermined points by an automatized coupling method. In addition, a 1D transient vehicle analysis is used to provide transient boundary conditions for the 3-dimensional vehicle. This 1D analysis provides the inputs for the cooling system, exhaust system, oil circuit, and the heat release inside of the engine combustion chamber. As a first step a computation of the heat-up during a trailer towing uphill drive at 35 km/h is performed and validated with experimental data. For this purpose, extensive heat-up measurements are conducted in a climatic wind tunnel. The car was preconditioned at 30°C and at the end of the test all relevant components reached a constant temperature. Comparing simulation results of the transient heat-up with measurement, the computational methodology is yielding to an encouraging agreement; especially for temperature-sensitive components like the engine mounts and actuators next to the turbocharger. In conclusion, it can be said that transient numerical coupling methods are capable of simulating the heat-up of the engine, the exhaust system, and temperature-sensitive parts in the underhood. In particular, detailed flow modeling of the exhaust flow and the coolant and oil circuit is the major key. Especially the surrounded parts in the engine compartment can be fairly good simulated according to measurements in the climatic wind tunnel.