Lubricants 101: The properties of lubricating oils – Part 1

Why do we need to lubricate? In this first part of a two-part introductory primer on industrial lubricants, we take a closer look at the need for lubrication and the key properties of lubricating oils. Regardless if you’re a seasoned pro or a new aspiring talent in this industry, this article will help you understand their significance when choosing the right lubes with the right characteristics for various industrial activities.

Oft-regarded as the lifeblood of machinery, lubricants are an essential component across multiple industrial activities. From bearings to engines to hydraulics, they are used to keep industries running smoothly by:

  • Lessening wear and tear
  • Reducing friction
  • Removing heat
  • Preventing rust and corrosion
  • Removing contaminants

Regardless if you’re a seasoned pro in the industry or a new aspiring talent, below is a guide on the basics of mineral and synthetics lubricating oils, beginning with its properties, to help you gain a firmer grasp of this essential industrial component.

1. Viscosity

Viscosity is defined as the fluid’s internal resistance to flow. The higher the viscosity of the fluid, the slower it flows. If you want your film to stay put at lower speeds, you need higher viscosity.

Considered the most important property of a lubricant, viscosity serves to form a lubricating film, cool machine components, and seal and control oil consumption. It has to be balanced for load, temperature and speed. Below is a table to illustrate how each factor affects how high or low a viscosity should be.

Chart about lubricants

Recognising Viscosity Designations

Viscosity is measured differently according to their designations by different groups:

chart about lubrication

Viscosity Chart

This chart illustrates the various lubricant viscosity grades, and if you read each line horizontally, the viscosity designations are equal.

viscosity chart

Viscosity Index (VI)
Viscosity Index (VI) is the rate of change of an oil’s viscosity with temperature. The higher the VI, the less an oil’s viscosity changes with temperature.

Viscosity index

Note: The numbers in the parenthesis are unitless numbers that show the difference between viscosity at 40 degrees Celsius and 100 degrees Celsius.

In the graph above, notice that the slope of each line is different over the same temperature range, depending on its viscosity: the lowest VI has the highest slope; the highest VI has the least slope.

 2. Thermal Stability

Thermal stability refers to the ability of lubricants to resist breakdown at high temperatures. Poor thermal stability can result in sludge, deposits and increased viscosity.

 3. Oxidation Stability

Oxidation stability refers to the ability of a lubricant to resist the chemical combination with oxygen. It can result in the creation of sludge deposits and increased viscosity.

Oxidation stability is accelerated by heat, light, metal catalysts, acids formed by water contamination and other contaminants.


4. Pour Point

Pour point is the lowest temperature at which an oil will flow under prescribed test conditions. It is affected by the amount of wax particles removed during the processing of crude.

The more wax particles there are, the higher the pour point. The fewer wax particles there are, the lower the pour point.

5. Demulsibility

Demulsibility is another important property of lubricating oils. It is the ability of an oil to separate from water.


6. Flash Point

Flash point is determined by heating the oil until vapours form; a flame is then passed across the oil. The flash point is the temperature at which the oil sparks, but a flame is not sustained.

The flash point for lubricating oils is typically 204°C (400°F) or above.

7. Fire Point

Fire point is determined in a manner similar to flash point. Oil is heated until vapours form; a flame is then passed over the oil. The fire point is the temperature at which the oil sparks and the flame is sustained.

The fire point for lubricating oils is typically 371°C (700°F) or above.


Next week, we will take a look at what are the various elements that need to be lubricated.

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