In which scenario would oil lose its utility?

Oil loses its utility primarily when mixed with water or other fluids because this contamination affects its lubricating properties and can lead to corrosion and rust within an engine or machinery. Oils are specifically formulated to maintain their viscosity, reduce friction, and protect metal surfaces. When water enters the oil, it can create an emulsion, leading to a significant reduction in performance efficiency.

In addition to the immediate loss of lubrication, water mixed with oil can lead to the formation of sludge and other deposits that can further degrade the effectiveness of the oil, damaging machinery and reducing longevity.

Storing oil for too long can impact its quality due to potential oxidation, but proper storage practices can mitigate this issue. Similarly, while extreme temperatures can affect oil's viscosity and performance, most oils are designed to withstand a range of temperatures. When used for engine lubrication, oil serves its purpose effectively, provided it hasn't been contaminated or degraded by other means. Therefore, the scenario where oil becomes ineffective due to mixing with water stands out as the clearest reason for it losing its utility.