Which condition requires further investigation in a reciprocating engine?

The discovery of small, bright metallic particles in the oil of a reciprocating engine is a condition that necessitates further investigation. This is because bright metallic particles often indicate that there is wear occurring on internal engine components, such as bearings or cylinder walls. The presence of these particles suggests that metal is being ground off due to excessive friction or improper lubrication, which can lead to serious engine damage if not addressed promptly.

In contrast, while dark oil can indicate contamination or the presence of byproducts from combustion, it is not necessarily a definitive sign of immediate internal failure. Bearing noise during startup can also warrant attention, but it may not always indicate critical failure or damage that requires urgent investigation. Exhaust discoloration can point to issues like burning oil or fuel-air mixture problems, but again, it does not have the same direct implication of imminent physical wear as bright metallic particles. Thus, the presence of these particles stands out as particularly concerning for the integrity of the engine.