A few hours after changing the oil on one of the diesel generator set engines on your offshore supply vessel, you notice that the oil is significantly darkened. What does this normally indicate?
• Behavior of diesel engine lubricating oil after an oil change • What causes fuel, water, or soot contamination in lube oil and how each typically appears • What is considered normal vs. abnormal oil appearance a few hours after running a diesel
• Think about what happens inside a diesel engine’s cylinders during normal operation and what by‑products can end up in the crankcase oil. • Consider which type of contamination (fuel, water, or soot) would usually change not only the color but also the consistency and appearance of the oil (milky, thin, thick, foamy, etc.). • Ask yourself: after several hours of operation on fresh oil, what change in color would a mechanic usually expect to see if nothing is wrong?
• Compare typical signs of water contamination (color and texture) versus just dark color. • Consider how diesel fuel dilution usually affects oil level, smell, and viscosity, not only color. • Recall that in diesel engines, some unburned carbon from combustion often ends up in the oil over time—decide whether that is normally a fault condition or an expected one.
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