The aim of the present article was an attempt to compare the influence of the presence of a diesel particulate filter (DPF) on the content of contaminants (Fe, Cr, Ni, Pb) and the level of changes of physical and chemical parameters (such as kinematic viscosity, TBN, TAN) in engine oils during their service life. The article presents changes occurring in engine oils at various stages of use. Medium infrared Eralitics ERASPEC OIL FT-IR spectrometer and XOS HDMaxine (powered by High Definition X-ray Fluorescence) were used. Based on the conducted experiment, statistically significant differences in diesel fuel content were noticed.