This paper introduces an innovative approach, named synergetic 1D-3D-Coupling, by using synergy effects of 1D and 3D simulation in order to bring down modeling and simulation efforts. At the same time the methodology sustains the spatial resolution of a 3D model. This goal is reached by reducing the 3D fluid side with its time consuming continuity, momentum, energy and turbulence equations to a simple but precise 1D model. Because of the solid structure staying three dimensional, heat flux direction and spatial resolution have 3D accuracy but short calculation times due to the simple heat diffusion equation to be solved. The 1D model is represented by an automatically generated equation system which is capable of considering transient effects. The energy transfer between 1D fluid model and 3D structure model is realized through a neutral 1D-3D-coupling program and the application of the fluid element specific Nusselt correlations.The following approach is not only applicable for engine development but for any field where fast transient CHT simulations of internal flows are needed.The theoretical background and the newly developed approach are presented in this paper. For this purpose an abstract pipe system is used to generate a hydraulic and thermal network. This network is coupled with a 3D structure in order to show the potential velocity benefit and the possible loss in accuracy compared to the conventional full 3D modeling approach.