Question 46 OSE01 - Chief Engineer - OSV

The Correct Answer is C **Why Option C is Correct:** When checking the crankcase oil level on a running, hot engine (such as a main propulsion engine underway), the goal is to maintain the oil level within the engine manufacturer's specified operating range. This range is universally indicated on dipsticks by marks designating the "FULL" (or MAX) and "ADD" (or MIN) limits for normal operation. The engine manufacturer designs the lubrication system (including the size of the oil pan, pump capacity, and de-aeration space) based on maintaining the oil level within this operational zone. Maintaining the level **between the FULL and ADD marks** ensures: 1. **Adequate Supply:** There is enough oil available for the pump to draw from and circulate throughout the engine. 2. **Proper Sump Clearance:** The level is not so high that the rotating parts (like the crankshaft throws) excessively churn the oil (aeration), which causes foaming, overheating, and loss of lubrication effectiveness. 3. **Correct Indication:** Since the engine is running and the oil is hot, some oil is distributed throughout the system (heads, filter, coolers, turbochargers), meaning the measured level is the true dynamic operating level. **Why the Other Options are Incorrect:** * **A) The actual level is unimportant as long as it is visible on the dipstick when the engine is running.** This is fundamentally incorrect and dangerous. If the level is too low (just barely visible), the engine risks oil starvation or damage due to insufficient reserve or the pump sucking air during movement (vessel pitch/roll). If the level is too high, aeration and foaming will damage the engine. The actual level relative to the established marks is critically important. * **B) The level should be well above the FULL mark on the side of the dipstick marked with engine IDLE and oil HOT.** Operating the oil level above the FULL mark introduces several serious problems: excessive oil consumption, oil foaming (aeration) caused by rotating crankshaft parts splashing into the high level, excessive pressure leading to seal leaks, and potential carryover of oil vapor into the air intake system. * **D) The level should be below the ADD mark on the side of the dipstick marked with engine IDLE and oil HOT.** The "ADD" mark (Minimum safe operating level) indicates that oil must be added immediately. Operating below this level means the engine lacks the necessary reserve volume, increasing the risk of oil starvation, overheating, and severe mechanical damage, especially if the vessel encounters heavy motion (pitch and roll).