In an Internal Combustion (IC) Engine, the exhaust manifold has the primary function of channeling unburned fuel and residual hot gases from cylinder head runners to the emissions system through a collector. Exhaust manifolds must endure severe thermal loads caused by channeling extremely hot gases, and high strain due to fastener loads. The combination of these two loads can lead to Thermomechanical Fatigue (TMF) failures after repeated operational cycles if they are not assessed and addressed adequately during the design process. Therefore, it is vital to have a methodology in place to evaluate the life of an engine component (such as the exhaust manifold) using a TMF damage prediction model. To accomplish so, spatial temperature prediction and maximum value attained, as well as temporal distribution, are the most important input conditions. The aim of this work is to generate the transient thermal field in the exhaust manifold and other metal components of an IC engine during a typical thermal fatigue test schedule, using commercial Computational fluid dynamics (CFD) tools. A time-based interpolation scheme was used to adjust convective conditions as the engine alternates between high and low operating loads during this test schedule. Finally, metal skin temperatures transiently recorded at thermocouple locations were compared with those from dyno test and good correlation was observed. The usage of this methodology leads to reduction of expensive dyno tests, and at the same time, shortening of exhaust manifold design and development time. The data obtained aids in the prediction of TMF induced failure of components (such as the exhaust manifold) subjected to severe thermal cycling. Calculation of life assessments using TMF damage models are covered in a separate paper.