COMPARATIVE TRIBOLOGICAL ANALYSIS OF NEW AND USED DIESEL ENGINE OILS

Abstract

This study investigates the tribological behaviour of aluminium samples lubricated with new and used SAE 10W-40 and SAE 30 engine oils under controlled laboratory conditions. Tribological testing was performed using a block-on-disc configuration on a TPD-95 tribometer, following ASTM G77 standards. All tests were conducted at a sliding speed of 0.5 m/s, an applied load of 20 daN, and a test duration of 600 seconds, with continuous lubrication provided. Results show that, for both oil types, the used oils exhibited a lower coefficient of friction compared to the new oils throughout the entire sliding distance. In the case of SAE 10W-40, used oil led to both reduced friction and significantly lower material loss, while in the SAE 30 group, despite lower friction, the used oil resulted in a slightly larger wear scar and increased worn volume compared to the new oil. These findings suggest that oil degradation products can temporarily enhance lubrication performance but may compromise long-term wear protection