bearing wear can be caused by high lubricant temperature thinning the oil. Which condition would most likely contribute to this wear?

• A. Water in the lubricant
• B. Low operating temperature
• C. High operating temperature
• D. Normal operating temperature

Answer: (C)

The key idea is that oil viscosity drops as temperature rises, thinning the lubricating film that keeps bearing surfaces separated. When the oil film becomes thinner, metal-to-metal contact increases, raising friction and wear on the bearing. Among the options, operating at a high temperature directly causes the lubricant to lose viscosity and the film to weaken, making bearing wear most likely. At low or normal temperatures, the oil is thicker and provides a stronger protective film, so wear from thinning is less likely. Water in the lubricant can cause wear too by diluting additives and causing corrosion or emulsification, but it doesn’t describe the thinning of the oil due to heat.