When the biodiesel enters the crankcase, its degradation can lead to the formation of organic acids and polymerisation, to the point of clogging the system and the internal combustion engines. Therefore, this article proposed the study of lubricant oils in order to trace its biodiesel contamination. The results showed that in relation to the viscosity at 40 C there was reduction above the limit allowed for some samples. The viscosity index results showed considerable changes. Using infrared spectroscopy was noted that the contamination by fatty acid esters does not follow a pattern related to time of use in the motor. However, as the lubricant oil samples were used, they probably contain degradation products that altered the levels of oxygenated compounds. For this reason, the mass spectrometry coupled to gas chromatography quantified the predominant oil and fat steroids contents and confirmed the contamination by biodiesel.