Lubricant Viscosity Explained
Every type of fluid possesses differing amounts of resistances against deformation. The measure of that resistance is called viscosity. Viscosity expresses the fluid’s resistance against either tensional stress, or shear stress.
A lubricant’s viscosity and how it changes under different temperatures and operating conditions is one of the most important properties that determines lubricant performance and protection.
Viscosity can be viewed in two ways:
What does it mean to motorists? The lubricant’s viscosity at 40ºC and 100ºC is used to calculate its viscosity index (VI) a measure of how much the viscosity of the fluid changes due to temperature. As we said, viscosity change due to temperatures and operating conditions influences performance. A lubricant that undergoes little viscosity change will generally perform better. A high VI indicates the fluid undergoes little viscosity change due to temperature fluctuations, while a low VI indicates a relatively large viscosity change.
Synthetic fluids generally have much higher viscosity index numbers compared to conventional fluids, meaning they provide improved protection to critical components over a wide range of temperatures. VI is normally reported on the oil’s product data sheet, like this one.
AMSOIL synthetic lubricants boast high VI numbers, meaning they’re more stable than competitive lubricants, so you can count on them to deliver outstanding protection.