What is an indicator of fuel quality deterioration?

The presence of water in fuel serves as a significant indicator of fuel quality deterioration because water contamination can lead to several issues. Water in fuel can cause microbial growth, which can produce sludge and varnish that clog filters and injectors, impairing the fuel system's operation. Additionally, water reduces the effective energy content of the fuel, leading to incomplete combustion and thus reducing engine performance. This can result in rough engine operation, increased exhaust emissions, and potential long-term damage to engine components.

Change in color, higher efficiency, and improvement in smell do not reliably indicate the quality of fuel. They might not correspond to actual performance or chemical integrity. For example, a color change can happen for many reasons that might not be related to water contamination or degradation in fuel quality.