This publication covers the development process of a thermal model within a complete longitudinal vehicle simulation. Therefore a dynamic/forward simulation within MATLAB Simulink is used. The modeling of the heat transport in the cooling circuit and the lubrication system as well as the heat input by the internal combustion engine is the focus of research.In the first part various possible numerical solution methods for the heat transport model are analyzed and evaluated with regard to the accuracy of the system description and real time capability. The latter is important as functionalities should be able to be subsequently implemented in an engine control unit. In addition, a method for the modeling of the heat input of the internal combustion engine is evaluated. Finally, a validation of the heat transport and heat input model is performed, using a two-cylinder motorcycle.The results of these research activities show that improvements are still possible by a proper selection and assembly of components (pumps, thermostat, water-cooler, etc.), as well as by the implementation of a thermal management. The presented method for modeling a thermal system in MATLAB Simulink is able to prove this potential.