Question 50 MODE02 - Assistant MODU Engineer

The Correct Answer is C **Why option C is correct:** When a diesel engine suffers from piston seizure due to severe overheating, the internal components (piston, liner, cylinder head, and crankcase atmosphere) are at extremely high temperatures. Opening the crankcase inspection covers (or doors) immediately would allow a large influx of fresh oxygen-rich air to mix with the hot, flammable oil mist and residual gases inside the crankcase. This rapid introduction of oxygen to an ignition-source-rich and combustible atmosphere creates a significant risk of a secondary event, specifically a **crankcase explosion** (or 'hot spot' ignition). Standard operating procedure mandates that the engine must be allowed to cool down naturally (usually for several hours) to drop the internal temperatures below the auto-ignition point of the oil mist before any inspection covers are opened. **Why the other options are incorrect:** * **A) Scavenge pump should be immediately secured to prevent loss of lube oil:** The scavenge pump is responsible for removing oil from the sump. Securing the scavenge pump would be irrelevant to preventing oil loss due to an overheat seizure. More importantly, securing the main lube oil circulating pump (which supplies oil) is a critical step immediately after stopping the engine, but securing the scavenge pump specifically is not the primary safety concern related to the risk of a crankcase explosion. The focus must be on cooling and preventing secondary ignition. * **B) Ventilation system should be continued in operation for one hour for cooling:** Continuing to operate the crankcase ventilation system would draw more fresh air into the crankcase. While ventilation is generally used to keep the concentration of oil mist low, doing so immediately after a severe overheat (which creates localized hotspots and volatile gases) increases the risk by introducing more oxygen to the superheated components, potentially fueling a fire or explosion. The priority is to isolate the crankcase and allow the temperatures to drop safely. * **D) Explosion covers should be opened slightly to provide extra ventilation:** Explosion covers (or relief valves) are safety devices designed to relieve pressure during an internal explosion, protecting the crankcase structure. They are spring-loaded and should never be manually opened slightly, especially not after an overheat seizure. Opening them would, like option B, introduce fresh air and significantly increase the risk of ignition.