When selecting a synthetic grease for a customer, we often discuss oil viscosity and the implications of higher and lower base oil for their application. We decided to make it easier with a video explanation so our customers can better understand the centistoke (cSt) numbers on a data sheet. This test was conducted at room temperature.
Oil viscosity can vary and we wanted to show just how big the differences can be. All grease starts life as an oil. A grease is created when a thickener is added to a base oil giving a lubricant the ‘stay in place’ characteristics familiar with a grease. We can change the apparent viscosity of a finished grease by altering the ratio of thickener to base oil.
Simple fluids including most lubricating oils follow Newtonian behaviour whereby fluid viscosity remains constant as a function of shear rate. However when the oil is made into a grease things change, the grease would be non-Newtonian, a grease viscosity being highly dependent on the rate of shear, or the rate at which the adjacent layers of grease move relative to one another.
Now we suggest you take a look at the article Understanding Kinematic Viscosity to get to grips with what Kinematic Viscosity means.