Degradation and chemical change of longlife oils following intensive use in automobile engines

•The analysis of thirteen lifelong oil samples in terms of their service life.•Inadequately monitored onboard computer parameters for the evaluation of oil state.•Observation of unwanted substances (water, fuel etc.) in the used oils.•Evaluation of the vehicle cooling system on the basis of the used oil state.

The paper researches the features and quality of longlife oils after the point of being recommended for replacement by the onboard computer. The longlife oils have their service life prolonged to 30 up to 50 thousand kilometres which is being monitored and evaluated by the onboard computer. The onboard computer then, on the basis of several parameters, modifies the interval to optimum value. Kinematic viscosity, TBN, the amount of soot, oxidizing and sulphating products, water, fuel, glycol and high antioxidant presence were measured. The results we obtained from the measurements do not correspond with the conclusions of onboard computers.