Everything you need to know about the properties of lubricating oils

From maximising the effectiveness of mechanical equipment in heavy-duty applications like gas and oil refineries to protecting engine components in conventional cars from dirt, rust, and other contaminants, lubricating oils are deployed in a wide selection of applications.

Picking the right lubricant is largely dependent on its physical and chemical properties. These will determine its performance characteristics and help users predict how a lubricant behaves during operation. This important information ultimately determines the capacity of a lubricant to answer specific requirements and meet set benchmarks.

Read on to discover everything you need to know about the properties of lubricating oils.


The term viscosity describes a lubricant’s resistance to flow. Viscosity is among the most vital properties to consider when assessing lubricants. Solutions with high viscosity are thick and deliver greater internal resistance in terms of flow. For instance, a steam cylinder oil used for lubricating heavy-duty engines needs to be highly viscous to cope with extreme operating conditions.

However, low viscosity lubricants are fast flowing and much thinner, operating in a similar way to water. An example of a low viscosity lubricant is kerosene, which is used for lubricating rolling metals.

Temperature impacts viscosity. As a result, many motorists use more viscous oils in their engines during colder weather. Sometimes, a lubricant’s viscosity will decrease when it is exposed to higher temperatures. In application where this is undesirable, additives may be included in solutions to mitigate the thinning process and ensure the sought-after viscosity index (VI) is retained.

Chemical stability

Another key property is chemical stability. Lubricating oils that have good chemical stability are not at risk of carbonising or oxidising when they are exposed to oxygen. A wide range of factors will determine a lubricant’s chemical stability. This includes the concentration of catalysts.

Sulphur content

An important physical property of a lubricating oil is its sulphur content. The reason for this is because the chemical element has the capacity to speed up corrosive processes. However, sulphur is also sometimes added to specific types of oils to enhance their lubricating capabilities.

Oxidation stability

The chemical reaction that takes place when oxygen and a lubricating oil interact is called oxidation. Variables like acids, water, temperature and catalysts can influence and impact oxidation levels and have a negative effect on the performance characteristics and lifespan of an oil. For applications where the lubricating oil is in circulation for extended periods without a change, as is often the case in large mechanical systems, excellent oxidation stability is crucial.


The term demulsibility describes the capability of a lubricating oil to efficiently separate from water. Oils that have high demulsibility are typically preferred because water can compromise a product’s lubricating properties. This can result in several unwanted issues like increased energy consumption because of resistance, as well as contamination and corrosion from the release of wear particles. The inclusion of additives is a suitable way to enhance the demulsibility of a lubricating oil and prevent it from combining with water.

Pour point

The lowest possible temperature at which a lubricating oil will continue to flow in its liquid form is referred to as its pour point. This important property determines the suitability of a lubricating oil for use in cold operating conditions and climates and when pressure is not being applied. Sometimes pour point depressants are used that decrease the solidification temperatures of oils and enhance performance.

Corrosion resistance

Corrosive forces occur when electrochemical activity occurs on refined metal. This chemical reaction deteriorates metal surface over time and regresses refined metal to a stable form like an oxide, hydroxide, sulphide or carbonate.

Cloud point

When working at low temperatures, lubricating oils can start to alter, changing from a liquid to a solid state. When this happens oil particles start to solidify and take on a cloudy appearance. Cloud point refers to the highest temperature when this process will occur.

Flash and fire points

The flash point of a lubricant refers to the lowest temperature required to ignite it if it meets a small naked flame. The ‘flash’ happens when light particles within the lubricant are volatised. Lubricating oils with high flash points are mostly preferred as they are far less likely to ignite during normal operating conditions and temperatures.

Fire points build on flash points and sees the lubricant exposed to increased heat. The fire point of a lubricating oil is described as the lowest temperature at which a lubricating oil will burn continuously burn. Like flash points, fire points that are higher are more desirable as they can reduce the risk of an oil burning while in circulation.

Freezing point

Finally, lubricants that have low freezing points are typically more useful as they will continue to function effectively across a full range of operating conditions and temperatures. For instance, a lubricant that possesses a low freezing point will not lose functionality if the temperature of its operating environment drops unexpectedly.

Automotive Lubricant

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