During the usage of lubricating oil, it will age, deteriorate, and lose efficiency due to its mixing with foreign matters that contain metal powder, filings, and other oils as well as additives, which result to changes in its chemical and physical properties compared to those of the virgin oil. The results showed that carbon residue and ash content for used oils increase when compared to those of the new one, but after vacuum distillation, it was decreased to 0.47 wt. %, and 0 wt. % respectively. The results of the determination of metals content (Iron, copper, magnesium, zinc, and manganese) demonstrated that there is an increase in the values for Fe, Cu, and Mg at the beginning of use and then settled off whereas no significant change was observed for additive elements (Zn and Mn) in virgin and used oil samples.
