Question 26 MODE01 - Chief MODU Engineer

The Correct Answer is A **Explanation for Option A (piston ring blow-by):** Piston ring blow-by occurs when combustion gases (which contain soot, carbon particles, unburnt fuel, and water vapor) leak past the piston rings and enter the crankcase. The increased load of combustion byproducts (primarily soot/carbon) entering the lubricating oil significantly increases the rate at which the oil becomes contaminated. This heavy contamination quickly loads the lube oil filter cartridge, causing it to reach its saturation limit (and trigger a bypass indicator or restriction warning) much sooner than normal. Therefore, a noticeable decrease in the time interval between filter replacements directly indicates excessive contamination, most commonly caused by piston ring blow-by in a diesel engine. **Why the other options are incorrect:** * **B) dirty air filter:** A dirty air filter restricts airflow, leading to incomplete combustion (rich mixture) and increased smoke/soot production. While this increased soot *does* contaminate the oil and accelerate filter blockage, the primary mechanism of introducing that heavy contaminant load into the oil stream is still often through blow-by (the soot gets into the cylinder and then past the rings) or by being washed down from the cylinder walls. However, option A (blow-by itself) is a more direct indicator of the physical pathway introducing the contaminant load into the crankcase and is a more common underlying fault associated with rapid filter clogging than just a dirty air filter alone. * **C) excessive oil temperature:** Excessive oil temperature accelerates the oil's thermal degradation (oxidation) and reduces its viscosity. While degraded oil might form sludge or lacquer, which could eventually affect filter life, it typically does not introduce the massive amount of hard carbon and soot particles required to rapidly clog a filter cartridge in a short time frame. * **D) excessive oil pressure:** Excessive oil pressure might potentially stress the filter housing or relief valve, but it does not introduce external contaminants into the oil stream. If oil pressure is excessively high, it usually relates to issues like a malfunctioning relief valve, high oil viscosity, or restricted flow *after* the pump, not the rapid accumulation of particulate matter that necessitates early filter replacement.