Which property must a lubricant maintain when temperatures change?

A lubricant must maintain its viscosity when temperatures change because viscosity is a measure of a fluid's resistance to flow and its ability to create a lubricating film between surfaces. As temperatures increase, many lubricants tend to become thinner, meaning their viscosity decreases. Conversely, when temperatures drop, lubricants can become thicker, increasing their viscosity.

It is crucial for a lubricant to operate within a specific viscosity range to ensure that it effectively reduces friction and prevents wear between mechanical parts. If the viscosity changes too much due to temperature fluctuations, it can lead to inadequate lubrication, excessive wear, or even failure of the machinery.

While other properties like flash point, corrosiveness, and color are important for other reasons, they do not directly influence a lubricant’s ability to function effectively under varying temperature conditions. Flash point relates to flammability, corrosiveness concerns chemical reactions with materials, and color often indicates the condition of the lubricant but does not impact its lubricating properties in the way viscosity does.