Viscosity modifiers, also known as viscosity index improvers, are an important part of modern lubricant technology. Multi-grade oil products contain viscosity modifiers to maintain a consistent viscosity across a wide range of temperatures. They thicken fluid in higher temperatures, while thinning it in lower temperatures. Engine oils, gear oils, power steering fluids, hydraulic fluids, and automatic transmission fluids can all include viscosity modifiers.
What is Viscosity?
Viscosity is a physical property of a fluid, defined as its resistance to flow. A fluid's viscosity is highly dependent upon temperature. Lubricant viscosity is closely related to its ability to reduce friction.
Usually, the industry desires the lowest viscosity lubricant that still forces two moving surfaces apart from one another. If the lubricant is too thick and has a consistency like honey, it requires a large amount of energy to pump or move. If it is too thin, the surfaces will rub, friction will increase, and wear will result.
It is well known that the viscosity of oil increases (thickens) as temperatures decrease and decreases (thins) as temperatures increase. The most common way of measuring the viscosity of lubricants is the kinematic method. This is performed by timing a known volume of oil as it flows through a calibrated capillary tube under gravity.
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.
Viscosity modifiers, also referred to as viscosity index improvers (VII), are polymers used to decrease the viscosity-temperature dependence of lubricant viscosity. VIIs allow for lighter base oils to be used as they make the oil act “thicker” at higher temperatures to prevent metal surfaces from rubbing together. Meanwhile, the oil remains thin at lower temperatures, allowing easier cranking and pumpability throughout the engine.
Multi-Grade Oils
Lubricants containing a VII are labeled as multi-grades or multi-viscosity oils. An example is an SAE 15W-40, where the “15W” represents the winter grade performance and the “40" represents the high temperature performance.
A characteristic of a quality engine lubricant is its ability to “stay-in-grade” during its useful life. Soot particles can conglomerate and thicken oil over time. High quality lubricants contain advanced detergency and dispersancy chemistry to prevent soot particles from binding together.
A lubricant can also thin (lose viscosity) and allow excessive wear if its VII fails. People commonly refer to this as “shearing,” which describes the shearing of long chain molecules. Shearing results in temporary and permanent viscosity loss.
We provide engine oils with unique soot-dispersing technology that stops oil from thickening. Our oils also use the latest VII chemistry to prevent thinning. FS Suprex Gold ESP stays in grade at ideal viscosity levels long after lesser oils fall out of grade. Talk to your local FS Energy Specialist for more information today.