Lube oil viscosity is a measure of the oil's internal resistance to flow,

 Lube oil viscosity is a measure of the oil's internal resistance to flow, and is one of the most important properties of a lubricant. It's important to choose the right viscosity oil for your engine, equipment, or machinery because the wrong viscosity can lead to excessive wear, fatigue, or engine failure. 

Here are some things to consider when choosing a lube oil viscosity: 

Temperature

For cold weather, choose an oil with a lower first number, like 5W or 0W. For hot weather, choose an oil with a higher second number, like 40 or 50. 

Operating conditions

Consider the operating and climate conditions in which the oil will be used. 

Oil weight

Take the weight of the oil into account when choosing the right one for your engine. 

Viscosity index

The viscosity index (VI) of a lubricant is determined by measuring the oil's kinematic viscosity at 40°C and 100°C. A traditional mineral oil has a VI between 95 to 100. 

Viscosity can be measured in several ways, including:

Shear stress and shear rate

Time required for an oil sample to flow through a standard orifice at a given temperature

Kinematic viscosity

SUS a

t 100 °F and 210 °F