Aerodynamic design and thermal management are some of the most important tasks when developing new concepts for the flow around tractor-trailers. Today, both experimental and numerical studies are an integral part of the aerodynamic and thermal design processes. A variety of studies have been conducted how the aerodynamic design reduces the drag coefficient for fuel efficiency as well as for the construction of radiators to provide cooling on tractor-trailers. However, only a few studies cover the combined effect of the aerodynamic and thermal design on the air temperature of the under hood flow [8, 13, 16, 17, 20].The objective of this study is to analyze the heat transfer through forced convection for a scaled Cab-over-Engine (CoE) tractor-trailer model with under hood flow. Different design concepts are compared to provide low under hood air temperature and efficient cooling of the sub components. The measured data have been used to validate the computational simulations performed with STAR-CCM+.At first, the experimental and numerical investigation of a transitionally rough surface on a flat plate with zero pressure gradient at high Reynolds number is presented to understand more about the boundary layer profile and skin friction coefficient. Furthermore, a generic study examines the temperature field of the near-wake flow for a heated surface-mounted block.In the main experimental and numerical part of the work, some first results of the heat transfer for the scaled tractor-trailer model with under hood flow are given. In the experiments, hot air has been generated by flowing through a heated scaled radiator to investigate the effect of the under hood mass flow by covering the inlet. For the standard configuration the measured air temperature distribution after the heat exchanger and under hood side wall inside the engine compartment as well as the drag coefficient has been compared to the numerical results.