Why is oil cleanliness important in lubrication and how is it measured?

• A. Contaminants accelerate wear; measured by ISO cleanliness codes (e.g., by particle counts) and oil analysis.
• B. Contaminants improve performance; measured by color coding.
• C. Contaminants have no effect; measured by viscosity only.
• D. Contaminants accelerate wear; measured by oil color.

Answer: (A)

Oil cleanliness matters because even small particles can become abrasive in the lubricating film, accelerating wear, scoring bearings, clogging filters, and shortening component life. Keeping oil clean reduces abrasive wear, helps pumps and filters function properly, and improves reliability.

Measuring cleanliness is done with standardized methods. ISO cleanliness codes express how many particles are present per milliliter in defined size ranges (for example, 4, 6, and 14 micrometers). This is usually determined by particle counting instruments or lab analysis. In addition, oil analysis checks for wear metals, water, and other contaminants to gauge overall oil condition and predict failures. Color or viscosity alone do not reliably indicate cleanliness, which is why quantitative particle counts and oil analysis are used.