Which of the following is NOT a common sign of lubricant contamination?

The presence of a consistent odor is not typically recognized as a common sign of lubricant contamination. While certain odors might arise from specific types of contamination, such as burnt oil or chemical breakdown, they are not universally applicable indicators like the other signs mentioned.

Discoloration, for example, is a clear visual cue that can indicate contamination, as lubricants may change color when exposed to contaminants or as they age. The presence of particles is another obvious sign, as foreign materials can accumulate in the lubricant, indicating that it is no longer pure or effective for its intended use. Additionally, increased viscosity can suggest contamination or degradation, as the lubricant’s ability to flow changes due to the presence of impurities or breakdown products.

Thus, while a consistent odor can provide clues about the state of a lubricant, it is not a standard or reliable measure for recognizing contamination as the other options are.