Emission regulations have become increasingly stringent in recent years. Current regulations need the development of a new worldwide driving cycle which gives greater weight to the pollutants emitted during transient phases or cold starts. Powertrains contain a large number of components such as multistage turbocharger systems; exhaust gas recirculation, after-treatment devices and sometimes an electric motor. In this context, 0D predictive models of heat transfer in the exhaust line, calibrated with experimental data, are particularly interesting. Many investigations are related to the development of precise control laws in order to optimize the light-off of after-treatment elements during the engine starting phase. A better understanding of the thermal phenomena occurring in the exhaust line is necessary.To study the heat transfer in the exhaust line of a Diesel engine during transient conditions, the temperature in the exhaust line must be known precisely. The experimental methodology followed by the authors contains three steps: first, temperature and pressure drops are made on a pulse generator to characterize properly each thermocouple (four different diameters). Then, the second step is to study the temperature during different types of transient tests on a Diesel engine equipped with an “empty” exhaust line (i.e. without any after-treatment system). Finally, the same tests are done on the engine equipped with a second exhaust line that contains a close-coupled DOC/DPF.Various types of tests have been performed on the test bench. Some of them are presented in this study : a quasi-steady state test which consists in starting the engine and stabilizing the engine speed and the IMEP at specific values, a transition test which consists in varying the IMEP while the engine speed is kept constant, and an ECE cycle with both engine speed and IMEP varying. The two first tests presented here have been done at a starting temperature of 15 °C, the ECE cycle has been carried out at a starting temperature of −7 °C. The next step is to use these tests and calibrations of the thermocouples to develop a methodology that calibrates heat transfer in a simulator of an exhaust line developed under Matlab/Simulink + AMESim platform.