The Difference between Kinematic Viscosity And Viscosity Index

Definition of kinematic viscosity:

Kinematic viscosity is an indicator of oil fluidity. Larger the value is , higher the viscosity will be; Smaller the value is, lower the viscosity will be. This value keeps changing with temperature. The higher the temperature is, the smaller the value and the lower the viscosity will be. On the contrary, the lower the temperature, the larger this value  and the higher the viscosity will be.

Summary of kinematic viscosity test method: Measure the time for the sample to flow through a calibrated volume viscometer at a certain temperature. The product of the measured flow time and the viscometer calibration constant is the kinematic viscosity of the sample (mm²/s). According to the formula calculation: v=C*t v is the kinematic viscosity, unit (mm²/s); C is the viscometer calibration constant, unit(mm²/s²); t is the process time, unit (s).

What does viscosity index mean?

In fact, it represents the degree to which the oil changes with temperature. The higher the viscosity index, the less the oil viscosity is affected by temperature, the less sensitive the viscosity is to temperature, and the oil can always maintain a stable viscosity. The viscosity index can be measured by testing equipment to determine the kinematic viscosity values of the oil at 40°C and 100°C.

The viscosity index represents the viscosity-temperature characteristics of lubricating oil. The higher the viscosity index is, the better the viscosity-temperature characteristics of the oil will be. In some ways, it means better oil quality. It is an important control indicator in the production process of lubricating oil manufacturers. Lubricants in my country are divided into three levels according to different viscosity indexes: 40-80 is an intermediate viscosity index; >80 is a high-grade viscosity index; >120 is a very high-grade viscosity index; >140 is a super-high-grade viscosity index lubricant.

Does the higher the viscosity index of lubricating oil means the better the quality of the oil? 

We need to know the viscosity index is a performance indicator of lubricating oil, not a quality indicator.

The selection of lubricating oil still depends on the operating conditions, not just the viscosity index. Different types of lubricating oils have different application surfaces, and the corresponding viscosity index requirements will be different, which has nothing to do with the quality of the lubricating oil itself. The selection of lubricating oil is related to temperature, speed, load and working environment. You still have to choose the lubricant that suits you based on the actual usage conditions.

Reference instrument:

Model	GD-265B	GD-265C	GD-265G	GD-265H
Temperature Range	Room temperature ~100℃, otherwise add ZL-1 refrigerator		-70℃~ room temperature	Room temperature ~100℃, otherwise add ZL-1 refrigerator
Temperature control precision	±0.01℃		±0.1℃	±0.01℃
Capillary type	Pinnacle capillary viscometer	Ubbelohde、 Pinnacle viscometer、	Pinnacle capillary viscometer
test holes amount	2	4	2	4
Timing	Wire controlled timing	metal button timing	Stopwatch	Touch screen + remote control
Structural features	single bath	Double-layer bath inside and outside	Double glazed heated glass	Integrated indoor and outdoor double-layer bath
Display Mode	LCD temperature control instrument			8-inch colorful high-definition LCD display
Calculation Mode	Manual	Manual	Manual	Auto
Others			Dual compressor refrigeration	With printing and data storage function