Viscosity
Pour point
Viscosity index
Base oil
The temperatures at which a lubricant operates and its viscosity have a direct effect on performance.
It is therefore critical to select lubricants with the working temperature of the machinery in mind.
Among the main characteristics of a lubricant, viscosity, viscosity index, pour point and base oil are especially affected by temperature. Understanding these parameters helps explain how temperature influences lubricant behaviour.
Viscosity is the most important property when choosing a lubricant: its ability to flow, or internal resistance to flow. When oil forms a film between a bearing and a shaft, some molecules are attracted to the shaft surface and others to the bearing — this is shear rate, directly related to viscosity and operating temperature.
If viscosity is too low, the oil film may fail and metal-to-metal contact occurs. If it is too high, flow resistance increases dramatically, causing overheating and oxidation. Selection must always match the service temperature range.
The temperatures at which a lubricant operates and its viscosity have a direct effect on performance.
It is therefore critical to select lubricants with the working temperature of the machinery in mind.
Engine oil viscosity is classified by the SAE scale. Winter grades carry the letter W; summer grades do not. Winter lubricants must meet low-temperature requirements while still performing at high temperature; summer oils only address hot conditions.
The stoke (St) is a unit of kinematic viscosity, often expressed in centistokes (cSt) at 40 degrees Celsius.
Pour point
Pour point is the lowest temperature at which the lubricant will still flow. To ensure fluidity in cold conditions, it should be at least 10 degrees Celsius below the recommended minimum service temperature. Otherwise, lubrication at start-up is inadequate, increasing friction, wear and failure risk.
Viscosity index
The viscosity index (VI) expresses how resistant the oil is to viscosity change with temperature. It is a key consideration where temperatures vary widely, especially in cold regions.
Temperature strongly affects viscosity: always consider the machinery working temperature when selecting a lubricant.
Base oil
Base oil is by far the main ingredient in a lubricant. Three types exist: mineral (from refined crude), synthetic (fully artificial) and semi-synthetic (a blend of both).
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