ISO 26422:2014 specifies a method of determining the shear stability of polymer-containing lubricating oils by the four-ball machine as specified in ISO 20623, but using a tapered roller bearing. The test results allow prediction of the in-service permanent viscosity loss.
NOTE Other International Standards exist which evaluate viscosity loss of polymer-containing oils. The method specified within this International Standard subjects fluids to a higher shear rate than, for example, the diesel injector nozzle shear test described within ISO 20844.[3] It is particularly appropriate for lubricants being used in high shear applications, such as components with gears and roller bearings. In such applications, the shear rate in the ISO 20844 test method can be too low to generate a realistic permanent loss in viscosity of the fluid.