Evaluation of Engine Oil Degradation: Enhancing Cost-Efficiency in Vehicle Fleet Maintenance

Vehicle fleet operators face many challenges. The most important of them are maintaining low operating costs, optimizing energy consumption, managing the risk of failure, maintaining high fleet efficiency, and meeting increasingly stringent environmental standards. An important role is to strive to eliminate undesirable losses of energy and materials resulting from improper lubrication of the combustion engine. This task can be made easier by regularly monitoring the physicochemical parameters of engine oil. The article aims to answer the research question regarding the degree of differentiation in the degradation of engine oil of the same viscosity and quality class, used in different types of vehicles and engine designs. The research material was engine oil in the SAE 10W40 viscosity class. The oil was used in four buses of the Municipal Transport Company. The buses differ in type (12 and 18 m) and engine design (2 different types). As part of the experimental work, the kinematic viscosity at 40 °C and 100 °C and the viscosity index were examined using the Stabinger SVM 3001 viscometer. Oil parameters were determined using the FTIR method, such as the degree of oxidation, nitrooxidation and sulfonation, soot and fuel content, degradation of additives, and acid and base number. Moreover, to examine changes in the content of elements responsible for oil additives, elemental analysis based on the HDXRF method was used. The test results showed that vehicle type and engine design influence oil degradation, considering these factors is crucial when choosing optimal oil service strategies.