Question 8 OSE02 - Assistant Engineer - OSV

The Correct Answer is C ### Explanation of Why Option C is Correct **C) The length of time that the engine has been shutdown** is the primary factor determining the necessity of pre-lubrication (pre-lube). 1. **Oil Film Collapse:** When a large engine is stopped, the pressurized oil film that separated the moving parts (especially main and connecting rod bearings) collapses. Due to gravity, the oil gradually drains out of the bearing clearances and oil galleries back into the sump. 2. **Dry Starting Risk:** If the engine is started without establishing a protective oil film, metal-to-metal contact (a "dry start") occurs in the first few revolutions. This causes severe wear, scoring, and potential catastrophic damage to the bearings and crankshaft journals. 3. **Manufacturer Specification:** Engine manufacturers specify a maximum allowable shutdown time (e.g., 4 hours, 8 hours, 12 hours, depending on engine type) after which the residual oil film is considered inadequate. If the engine has been stopped for longer than this duration, pre-lubrication (using an auxiliary pump to pressurize the system before turning the engine over) is mandatory to ensure a hydrodynamic wedge of oil is present upon ignition. --- ### Why the Other Options Are Incorrect **A) The interval of time since the last engine overhaul** While the engine's mechanical condition (how long it has been since an overhaul) affects overall performance and tolerances, it does not dictate the immediate need for pre-lube. Pre-lube is a preventative measure related to the current state of lubrication (i.e., whether the oil film has drained), not the historical maintenance schedule. A newly overhauled engine and an engine nearing its overhaul time both require pre-lube if they have been shut down for an extended period. **B) The viscosity of the lubricating oil** Viscosity (thickness) is critical for proper engine operation and flow, and it is affected by temperature (D). However, viscosity addresses the *quality* of the lubricant and its ability to maintain a film under pressure, not the *presence* of oil in the galleries. The primary determining factor remains the time elapsed since the pressure dropped to zero and the oil began draining. **D) The ambient temperature in the engine room** Ambient temperature is a significant secondary factor. If the engine room is very cold, the oil viscosity increases, making pumping more difficult and potentially requiring heating before starting. However, temperature does not change the fundamental fact that the oil film has drained away due to gravity over time. An engine that has been shut down for 12 hours requires pre-lube whether the engine room is 20°C or 40°C. The duration of the shutdown (C) remains the primary trigger.