Viscosity Index (VI)

Description

An empirical calculated indicator reflecting the degree of change in the kinematic viscosity of an oil depending on the temperature (temperature stability).

Temperature is the biggest enemy of any lubricant. When heated, oil becomes as thin as water, losing its ability to keep metal parts from rubbing, and in the cold, it thickens to the consistency of honey, blocking pumps. The Viscosity Index (VI) is an indicator of how bravely your oil withstands these temperature fluctuations. The RENA laboratory calculates this critically important parameter so you know exactly: whether your engine or hydraulics are filled with a premium product on a stable synthetic base, or a cheap mineral oil that will «break» at the first overheating. A high viscosity index is a guarantee that the lubricating film will remain strong in the heat and the fluid will not freeze in the winter. The viscosity index is not measured by a direct instrument; it is a calculated value computed using the complex formulas of the ASTM D2270 standard. To obtain this index, we use our ultra-precise Austrian Anton Paar viscometer (SVM 3001). The instrument automatically, with an error of no more than 0.1%, measures the kinematic viscosity of the same oil sample at two strictly specified temperatures: 40 °C and 100 °C. These two obtained points allow the construction of the fluid's temperature-viscosity curve. Using a built-in microprocessor, the system mathematically compares this curve with reference series of oils (historically taken as standards with VI=0 and VI=100) and outputs a dimensionless number. The less the oil thins out when heated from 40 to 100 degrees, the higher the final value of the viscosity index will be.