Describe two types of lubricant failure modes.

• A. Lubricant improves electrical conductivity.
• B. Lubricant degradation (oxidation, viscosity change) and contamination (water, dirt) leading to reduced film strength and wear.
• C. Lubricant causes corrosion of metal.
• D. Lubricant cannot fail.

Answer: (B)

The main idea is that lubricant failure happens mainly through two pathways: degradation and contamination. When a lubricant degrades, its chemistry and properties change—oxidation can form acids and varnish, and heat or shear can alter viscosity. A lubricant that becomes too thin or too thick can’t maintain a proper protective film between surfaces, so metal-to-metal contact increases and wear rises. Contamination introduces unwanted substances such as water or dirt into the lubricant. Water lowers film strength and can create emulsions, while dirt and wear particles act as abrasives, penetrating the film and speeding wear. Together, degradation and contamination undermine the lubricating film, leading to increased wear and potential failure of the system.

Other statements don’t describe the common ways lubrication fails. For example, conductivity isn’t a failure mode, and saying the lubricant cannot fail isn’t accurate, while corrosion is usually a consequence of contamination or oxidation rather than a direct, separate failure mode of the lubricant itself.