Which lubricant characteristic is determined by load, temperature, and speed?

The correct choice highlights viscosity as a critical lubricant characteristic influenced by load, temperature, and speed. Viscosity refers to the thickness or resistance to flow of a lubricant. As these external conditions change—such as an increase in load or operating temperature—the viscosity of the lubricant can change, affecting its ability to create an effective lubricating film between moving parts.

For instance, under higher loads, a lubricant may need to be thicker (higher viscosity) to prevent metal-to-metal contact. Conversely, at elevated temperatures, some lubricants may thin out (lower viscosity), which can lead to insufficient lubrication if not properly accounted for in the lubricant selection. In high-speed applications, maintaining the right viscosity is crucial to ensure that the lubricant can effectively separate moving parts and reduce friction and wear.

Other options, such as composition, thickness, and grease type, while relevant to the overall performance of lubrication, do not directly address the combined influence of load, temperature, and speed in the same way that viscosity does.