In this study, physicochemical characteristics of Pakistani fresh and used monograde (SAE-40, SAE-50) and multigrade (SAE-20W/50) engine oils have been studied. The samples were analyzed for specific gravity at 60/60°F, kinematic viscosity at 100 and 40°C, kinematic viscosity index, pour point, flash point, total base number, copper strip corrosion and sulphur contents following the ASTM (American Society of Testing and Material) standard methods. Five samples of automotive lubricating oils of different API (American Petroleum Institute) grades as mentioned above were included in this investigation. Samples were taken from the sumps of five different engines, that is, three spark engines, and two compression ratio diesel engines(one ordinary duty and other heavy duty engine oil) after covering several mileage of service (ranging from 800 to 2800 km). Results show the deterioration of the samples with increased reduction as the vehicle covers more distance with the same oil which needs to be replaced. Specific gravity increases with usage due to engine wear and induction of oxidation products. Viscosity of all samples decreases as the oil ages, which is due to lighter end contaminants. Pour point of monograde oil slightly decreases with usage but no change in pour point was found in more stable multigrade oil. Flash point and Total Base number decreases depending upon the usage of oil. Sulfur contents of used oil were recorded higher because of the presence of wear caused between the moving parts as the oil strength decreases with increased usage which then cannot prevent the friction among the moving parts of the engine.
Key words: Physico-chemical, characteristics, used engine oil, Pakistan.
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