Question 46 MODE02 - Assistant MODU Engineer

The Correct Answer is B **Explanation for Option B (Correct Answer):** Reducing the load and speed on the overheating engine is the appropriate initial response. This action immediately decreases the amount of heat being generated by the engine's combustion process, which is the root cause of the rising jacket water temperature. By lowering the thermal load, you buy crucial time for the cooling system to attempt to catch up, or at least slow down the rate of temperature increase, without causing immediate damage. This allows the engineering crew to diagnose the underlying cooling problem (e.g., loss of raw water flow, failure of a pump, or clogged heat exchanger) while maintaining some degree of control and avoiding a complete thermal shock shutdown. **Why the other options are incorrect:** * **A) Shut down the engine immediately.** While a complete shutdown will stop heat generation, an immediate emergency shutdown subjects the engine to severe thermal shock due to uneven rapid cooling, which can lead to warping, cracking of cylinder heads, or other component failure. An immediate, uncontrolled shutdown should only be performed if the engine is experiencing catastrophic failure (e.g., severe loss of lube oil pressure or mechanical knocking), not just an overheat condition, which can often be managed initially. * **C) Add makeup water to the expansion tank.** Adding cold makeup water to an already boiling hot system can cause thermal shock to hot metal components and often exacerbates the boiling condition (flash steam). Furthermore, the expansion tank sight glass already indicates "out of range (high)" because the boiling water is expanding and turning to steam; adding more water is unnecessary and potentially harmful at this stage. * **D) Drain water from the expansion tank.** Draining water would lower the system pressure and reduce the overall volume of coolant, accelerating the overheating process and potentially exposing the engine's highest components (like the cylinder liners or cylinder head surfaces) to steam, which is a very poor heat transfer medium compared to water. This would lead to rapid and catastrophic localized overheating.