Full definition
A predictive maintenance technique that examines samples of lubricating oil from operating machinery to detect: (1) Wear metals — iron, copper, chromium, aluminum, lead particles indicate component wear (spectrometric analysis, particle counting per ISO 4406). (2) Contamination — water content (Karl Fischer titration, max 200 ppm for most systems), dirt/silica (silicon content), fuel dilution, and coolant contamination. (3) Oil condition — viscosity change (ASTM D445), Total Acid Number TAN (oxidation indicator), Total Base Number TBN (depletion of additive package), oxidation, and nitration by FTIR spectroscopy. Trending oil analysis results over time reveals developing problems 2-6 months before failure, allowing planned corrective action rather than emergency repair. Sample correctly: from a turbulent flow point (not the drain), at operating temperature, using clean sample bottles, and at consistent intervals. Standards: ISO 4406 (particle counting), ASTM D6224 (in-service monitoring), and ASTM D7647 (trending). Laboratories: Polaris, TestOil, Wearcheck, Noria. Typical cost: $15-40 per sample — trivial compared to a bearing failure costing $5,000-50,000+ including downtime.