Which factor is crucial for determining the effectiveness of a grease?

The effectiveness of a grease is primarily determined by its oil content and mobility. The oil content is essential because it directly influences the lubricating properties of the grease, providing the necessary film strength and reducing friction between moving parts. Mobility refers to how easily the grease can flow to the areas that require lubrication, which is vital for ensuring that all components receive adequate coverage and protection against wear and corrosion.

While the cost, age, color, and smell of grease may provide some context or secondary considerations, they do not address the primary functions that define a grease's performance in mechanical applications. Cost can be a factor for budget considerations, age might affect the performance due to degradation over time, and color and smell may reflect the type or quality of ingredients but have little direct impact on lubrication effectiveness. Thus, understanding and evaluating the oil content and mobility are fundamental for determining how well a grease will perform in its intended application.