Which term describes a thermal condition above a specified limit that affects fluid viscosity?

• A. Over-pressurization
• B. Contamination
• C. Excessive heat
• D. Improper fluid

Answer: (C)

Viscosity changes with temperature, so when heat in the system rises above the specified limit, we call that excessive heat. This condition typically lowers the fluid’s viscosity, causing it to flow more easily but also reducing the lubricating film and changing flow characteristics. That shift can affect pump performance, valve operation, and seal life, which is why excessive heat is the right term for a thermal condition that impacts viscosity. Over-pressurization relates to pressure, contamination to impurities, and improper fluid to wrong type or compatibility—not to a temperature-driven change in viscosity.