Investigation of the rheological properties of waste and pure lube oils

•Both types of diesel lube oils show Newtonian flow behavior with slight apparent yield stress.•Shear stress, viscosity, and index are higher for the waste petrol oil than the pure petrol oil.•At high temperature, both petrol oils exhibit viscosity reduction showing non-Newtonian shear thinning.•Rheogram behaviors of Pure Motorcycle Oil are slightly higher than its Waste Oil for all temperatures.•Both of Waste Jet Oil & Pure Jet Oil undergo substantial viscosity descent with temperature. In this study, the rheological characteristics of the waste and pure lube oils were investigated experimentally. Studying these characteristics are useful for understanding the behavior of lubricants and the recycling of waste lube oils. The Fann Model of 50SL rheometer with coaxial cylinders was employed for this investigation. Four different types of waste and pure lube oils were examined, namely: diesel-, petrol-, motorcycle-, and jet-engine oils. The results from the study show that the viscosities of all types of lube oils decrease gradually with temperature and shear rate due to the reduction of the intermolecular forces, which leads to a decline in the flow resistance. At a specific shear rate of 100 s−1 and heating the oils from 50 °C to 90 °C, the viscosity drops almost 60% for pure & waste diesel lube oils, 60–64% for pure & waste petrol lube oils, 48–50% for pure & waste motor-cycle lube oils, and 50–60% for pure & waste jet lube oils, respectively. The well-known Arrhenius relationship was also utilized in studying the temperature effect of the apparent viscosity.