What is an indicator of possible bearing wear in an engine?

A change in oil color is indeed a significant indicator of possible bearing wear in an engine. As engine components wear, metal particles and other contaminants can enter the lubricating oil. This can alter the oil's color, typically leading to a darker or opaque appearance. Monitoring the condition of the oil is crucial, as it provides vital information about the internal state of the engine, including the health of bearings.

The other options relate to different aspects of engine performance and may not be as directly correlated with bearing wear. High oil temperature generally indicates issues such as inadequate cooling or excessive friction, both of which could be related to bearing problems but are not definitive indicators of wear. Increased lube oil pressure may suggest a blockage or an improvement in lubrication, but it does not directly link to bearing condition. Excessive vibration might signal various mechanical issues, including misalignment or imbalance but, like temperature and pressure, does not specifically indicate bearing wear without taking additional diagnostic steps. Thus, the color change of the oil serves as a more direct and observable sign of potential bearing troubles.