Viscosity modifiers, also known as viscosity index improvers, are an important part of modern lubricant technology. The viscosity modifiers help lubricants achieve appropriate “thickness” across a range of temperatures and speeds (shear). The grade of an oil will describe how the temperature will impact its viscosity. All oils thin out when they are heated and get thick when cold.
Monograde (single grade) oils are suitable for specific temperatures. Multigrade oils are suitable for a wide range of temperatures as they flow easier in cold temps and thin less as it warms. This is achieved by polymers in the oil.
The viscosity modifier molecules become more soluble in the oil as it heats up. They begin to unwind and interfere with the movement of the oil molecules effectively mitigating the impact of temperature. Multigrade oils essentially eliminate the need for seasonal changes.
For example, two primary roles of engine oils are to lubricate moving engine parts and reduce the friction and wear of metal surfaces. To perform these functions well, engine oils must exhibit acceptable viscosity characteristics throughout a broad range of engine operating temperatures and shear environments. This is achieved by inclusion of viscosity modifiers.
Engine oils, gear oils, power steering fluids, hydraulic fluids, automatic transmission fluids and greases can all include viscosity modifiers.
Not all viscosity modifiers are the same - some shear a great deal more than others while in service. We control and manufacture our own viscosity modifiers in-house at the GROWMARK Lubricants facility in Council Bluffs, IA. In our multigrade engine oils, we select the best shear stability technology viscosity modifiers we can produce to ensure stay-in-grade performance.
What is Viscosity and Viscosity Index?
Viscosity is a physical property of a fluid, defined as its resistance to flow. A fluid's viscosity is highly dependent upon temperature. Viscosity should be high enough to form the protective film, but low enough not to give excessive energy losses within the fluid
The Viscosity Index (VI) of a lubricant relates to the change in viscosity for a given change in temperature. VI is calculated using viscosities at 40º C and 100º C. A high VI lubricant will have a smaller change in viscosity with a given change in temperature than one with a low VI.
It’s important to look at all performance characteristics of an oil prior to choosing the right one for your application(s). Should you need additional guidance, talk to your local FS Energy Specialist for more information today.