Determination of Viscosity of Selected Lubricating Oils Used in Nigerian Automotive Industry

Lubricating oil viscosity is the most critical property governing film formation in engine bearings and cylinder liner contacts. In Nigeria's automotive service sector, which operates under demanding tropical temperature conditions, appropriate viscosity-temperature behaviour of engine lubricants is essential for engine longevity. This study determines the kinematic viscosity of five automotive lubricating oil brands widely sold in Kano, North West Nigeria, at temperatures of 40 and 100 degrees Celsius using calibrated glass capillary viscometers following ASTM D445 standard procedures. The viscosity index is calculated from the measured kinematic viscosities using the ASTM D2270 method. Total base number is also measured by potentiometric titration following ASTM D2896. Results indicate kinematic viscosities at 40 degrees Celsius ranging from 68.2 to 108.4 centistokes for the five oils, with viscosity indices of 98 to 142. Two imported brands show viscosity index values consistent with multigrade SAE 15W-40 classification, while three locally blended brands show viscosity index values 15 to 22 units below their labelled SAE grade, raising concerns about product consistency. Total base numbers range from 8.2 to 11.4 mg KOH per gram. Keywords: lubricating oil, viscosity, viscosity index, automotive, Kano