Question 47 MODE02 - Assistant MODU Engineer

The Correct Answer is C. **Explanation for Option C (Correct):** The discharge of a "rather large amount of water" from the cylinder test valves when rolling over a main engine indicates a serious breach of the combustion space by the cooling medium (jacket water) or, potentially, seawater if the engine uses raw water cooling passages near the combustion area (though jacket water is the more common culprit). Introducing non-compressible fluids like water into the cylinders leads to a high risk of **hydrolock** (hydraulic lock) and severe mechanical damage, such as bent connecting rods, cracked cylinder heads, or a completely seized engine, particularly during starting when full combustion forces are applied. Operating an engine with a known leak into the cylinder is extremely dangerous and could lead to catastrophic failure. Therefore, the engine must not be started until the source of the leak (e.g., a cracked cylinder liner, faulty cylinder head gasket, or damaged cylinder head) is located and properly repaired. **Explanation for Other Options (Incorrect):** * **A) Start the engine but run the engine with the cylinder test valves cracked slightly open.** Running the engine with the test valves open relieves pressure but does not solve the fundamental problem of water entering the cylinder. Furthermore, operating an engine under load with the test valves open compromises combustion efficiency, allows hot, high-pressure gases to escape dangerously into the engine room, and could still lead to component damage if the leak rate exceeds the expulsion rate. This is unsafe and poor operating practice. * **B) Start the engine but maintain the jacket water expansion tank level higher than normal.** The expansion tank level is only a symptom monitor. Adjusting the level higher does nothing to stop the physical path of water migration into the cylinder (the actual leak) and merely risks losing more water into the affected cylinder faster, potentially increasing the danger of hydrolock or overheating due to a rapidly dropping overall system level. * **D) Start the engine, but monitor all fluid levels very closely, especially that of the jacket water.** While monitoring fluid levels is always necessary, simply observing the symptoms while starting an engine with a known, severe leak is irresponsible. The mechanical damage caused by hydrolock happens instantly upon firing, often before any monitoring can alert the operator to the full extent of the danger. The priority must be preventing the damage, not merely observing it happen.