What is a viscosity Index (VI)?
All oils thicken with decreasing temperature & thin when increase it. Thin oil takes little energy to move, but gives minimal separation of surfaces, whilst thick oil gives good separation but uses energy to move shafts through the lube meaning machinery operating temperatures have a big impact on wear rates & energy efficiency, hence why lube oil manufacturers try to work towards a perfect oil that stays the same thickness (viscosity) with temperature. Base oil selection & additives give improvements to this property termed VI with high values indicating more stable viscosity. To find out more lube oil facts comment below.
Find out how viscosity is tested below, what is it’s significance and how to diagnose viscosity changes.