Lubricant Properties

Lubricants have a wide range of properties that impact their physical and chemical properties.  Knowing about these properties is important in determining which lubricant is best for which situation.  While there are many properties, the most important are:

1. Viscosity: A lubricant’s “internal resistance to flow.”  Higher viscosity lubricants are thick and don’t flow, while lower viscosity lubricants have a closer consistency to water and do flow.  The image below demonstrates the viscosity of four different oils.  The ball sinks faster in the thinner, low viscosity oil while it sinks slower in the higher viscosity blends.   

2. Viscosity Index: The rate of change in viscosity with changes in temperature.  In other words, how much viscosity changes as temperature changes.
3. Oxidation Stability: Oxidation is a reaction that occurs when oxygen is combined with lubricating oil. Variables such as high temperatures, water and acids will accelerate the rate of oxidation. The life of a lubricant is reduced as temperatures increase, leading to varnish and sludge.
4. Pour Point: The lowest temperature at which a lubricant will flow or pour like a liquid.  This can differ depending on test conditions. 
5. Demulsibility: The ability of a lubricant to separate from water.
6. Flash Point: The temperature at which a lubricant will ignite when heated and mixed with air, but a flame is not sustained.

While there are other properties to consider when choosing a lubricant, these are often considered the most important.