Historically, there were two different oil types recommended for usage in different weather conditions. This allows for consistent engine performance within the normal working conditions. The best oils with the highest VI will remain stable and not vary much in viscosity over the temperature range. Many lubricant applications require the lubricant to perform across a wide range of conditions, for example, automotive lubricants are required to reduce friction between engine components when the engine is started from cold (relative to the engine's operating temperatures) up to 200 ☌ or 392 ☏ when it is running. If the lubricant is too viscous, it will require a large amount of energy to move (as in honey) if it is too thin, the surfaces will come in contact and friction will increase. Generally, the least viscous lubricant which still forces the two moving surfaces apart to achieve " fluid bearing" conditions is desired. The viscosity of a lubricant is closely related to its ability to reduce friction in solid body contacts. The VI was originally measured on a scale from 0 to 100 however, advancements in lubrication science have led to the development of oils with much higher VIs. The higher the VI, the more stable the viscosity remains over temperature fluctuations. The lower the VI, the more the viscosity is affected by changes in temperature. It is mostly used to characterize the viscosity-temperature behavior of lubricating oils. The viscosity index ( VI) is an arbitrary, unit-less measure of a fluid's change in viscosity relative to temperature change. JSTOR ( May 2018) ( Learn how and when to remove this template message).Unsourced material may be challenged and removed. Please help improve this article by adding citations to reliable sources. On the contrary, low viscosity fluids are more volatile, creating environmental problems.This article needs additional citations for verification. Oils with too high viscosity don't protect well against mechanical friction, resulting in heat generation. Viscosity will affect the thickness of the oil film as well as the effectiveness of its protective qualities. These films are used to protect equipment from mechanical wear and may also have extra benefits such as creating a barrier to corrosion. The viscosity of oil and lubricants are often measured in industrial settings.
Kinematic viscometers determine the kinematic viscosity by measuring the time it takes for the fluid to pass through a portion of a capillary. Care must be taken when interpreting values and the temperature at which the values were measured. Understanding the distinction comes into play in industrial settings as record data is normally reported as kinematic viscosity, but onsite measurements are often measured as dynamic viscosity. Kinematic viscosity is not the same as dynamic viscosity, although they are related mathematically by the density of the fluid. This intermolecular friction is what makes the fluid resistant to change in shape and explains the thick and slow moving properties of highly viscous fluids. The stronger the intermolecular force, the more the molecules will stick together as they collide, manifesting a frictional interaction. Strongly polarized interactions like hydrogen bonding in water or interactions between large non-polar surfaces in viscous oils produce stronger intermolecular forces. Viscosity results from the intermolecular forces between molecules in a liquid. Corrosionpedia Explains Kinematic Viscosity