What is a common sign of fuel degradation?

A strong, sour odor is a common sign of fuel degradation because it indicates the presence of organic acids that form as fuel breaks down over time. This sour smell can suggest that the fuel has started to go bad due to oxidation or microbial contamination, both of which are concerns in fuel storage and handling.

Identifying this odor is critical for maintaining fuel quality, as it can impact engine performance and lead to operational issues. The presence of a sour odor serves as a warning to inspect and possibly replace the degraded fuel to prevent further complications.

Other signs of fuel degradation, such as unusual color changes and increased viscosity, can also be indicators, but the sour odor is particularly notable and typically easier to detect, which makes it an important aspect to monitor in fuel maintenance practices. The options related to taste are less relevant in a maintenance context, as taste is not a practical or safe method to assess fuel quality.