The increase in the energy efficiency of internal combustion engines has taken great importance in recent years due to the need to reduce fuel consumption and environmental impact. In this study, a parametric study assisted by CFD simulation has been carried out using the open-source OpenFOAM®, applied to a heat exchanger composed by a double concentric tube. It is made of copper, and the transport fluids are exhaust gases and Theminol-75 thermal oil. A diverse group of geometric configurations has been performed by varying the basic parameters of the heat exchanger, and the results obtained has allowed finding a set of equations and curves, whose mathematical model reveals flow and heat transfer characteristics, such as the Reynolds number, the Nusselt number, and the convective heat transfer coefficient h. The equations obtained from the curves have a very high degree of acceptance within the limits of this study, allowing the geometrical parameters to be varied within the standards established for commercial copper pipes. The results obtained show a degree of accuracy of 93% between the limit values as well as for the flow regimes and physical states of the matter indicated.