At conferences and seminars about bearings and bearing failures the talks center on the physical damage of the bearings themselves. Very little is said about the lubricant and lubrication methods. About 50% of bearing failures can be traced back to lubrication problems. Some are due to lubricant choices others are due to lubricant failure. How does a lubricant fail? How do you determine the health of a lubricant? This course will discuss failure modes of lubricants, including oxidation, degradation and contamination. The course will then proceed to discuss how these failure modes manifest in typical tests for used lubricants such as viscosity, acid level, water level, and contamination level.The presenter will introduce some common “rules of thumb” for when a lubricant has reached the end of service life and discuss their merits.