The paper presents the issues related to the unevenness of air filling inside a cylinder of a combus-tion engine. In order to evaluate such an unevenness a test stand and simulation models have been built. The tests stand allows a full assessment of the influence of selected parameters on the uneven-ness of the filling process. In this case the deviations in individual ducts of an intake manifold have been analyzed. This variant has been repeated in simulation tests, where concentrated models have been used for the description of the phenomena. The tests have shown an approximately 6% influence of a 64oC temperature deviation on the unevenness of the cylinder filling. The simulation tests have not shown a significant impact of the thermal state on the filling process