Which of the following is a property of good lubricants?

A good lubricant is characterized by its ability to maintain viscosity under varying temperatures. Viscosity refers to a fluid's resistance to flow, and it is crucial for lubricants to operate effectively across a range of temperatures. As temperatures rise, many fluids tend to thin out, losing viscosity. Conversely, in colder conditions, some lubricants can become too thick, which can impede performance. Therefore, a lubricant that maintains its viscosity across temperature changes ensures optimal performance and protection for machinery, reducing wear and tear.

High thermal conductivity, while beneficial in some applications, does not solely define a good lubricant, as excessive heat transfer may not always be desirable. The ability to evaporate easily and high volatility are properties that generally indicate poorer quality in lubricants, as they can lead to a quicker depletion of the lubricant and reduced effectiveness. Thus, maintaining viscosity is fundamental in ensuring lasting performance and efficiency in various operating conditions.