Temporary Viscosity Loss in Shear Stability Testing

The relationships between the permanent and temporary viscosity losses were examined for 43 oils at 100°C and 150°C. High-shear-rate viscosities were measured at a shear rate of 106 s^-1 in a capillary viscometer for new oils and used oils. New oils that had been subjected to 20 cycles in the Fuel Injector Shear Stability Test were considered to be used oils in this program. There was no useful relationship between the temporary viscosity loss (difference between kinematic and high-shear-rate viscosities of new oil) and the permanent viscosity loss (difference between kinematic viscosities of new oil and of used oil). Also, there was no useful relationship between either the temporary or permanent losses alone and the combined loss (difference between kinematic viscosity of new oil and high-shear-rate viscosity of used oil.) There was, however, a relationship between the temporary loss and the permanent loss, used together, and the combined loss. This relationship makes it possible to estimate the combined viscosity loss without having to measure the high-shear-rate viscosity of the used oil.