Question 5 UFIV02 - Assistant Engineer - UFIV

The Correct Answer is A **Explanation for Option A (Correct Answer):** The cylinder jacket water cooling expansion tank serves two primary purposes: to accommodate the thermal expansion of the cooling water as the engine heats up to operating temperature, and to ensure that the circulating pumps always have a positive suction head and remain fully flooded. When the engine is at operating temperature, the cooling water volume is at its maximum due to thermal expansion. Therefore, the level should be near the top of the sight glass (but not over-full) to indicate that the system has enough water to handle maximum operating conditions and that minimal air is present, while still allowing for a small safety margin against overflow. Maintaining the level in the upper part ensures optimal system capacity and prevents cavitation in the cooling pumps. **Explanation of Incorrect Options:** * **B) The level should be in the lower part of the sight glass when the engine is at operating temperature.** This is incorrect. If the level is in the lower part when the engine is hot and the water volume is maximized, it implies the system started with insufficient water or has lost a significant amount. This increases the risk of the cooling pumps losing suction (cavitation) or the engine overheating if the level drops further. * **C) The actual level is unimportant as long as it is visible in the sight glass when the engine is at operating temperature.** This is incorrect. The actual level is critical. If the level is only barely visible (e.g., at the very bottom), it indicates the system is running low. The level must be maintained within a specified range (typically the upper half) to guarantee proper functioning, pump suction head, and adequate reserve capacity. * **D) The level should be out of sight high in the sight glass when the engine is at operating temperature.** This is incorrect. If the level is out of sight high, it means the tank is completely full or overfilled. This eliminates the necessary air cushion (ullage space) required to accommodate any further expansion or surges, risking the expulsion of coolant through the vent or relief valve and potentially leading to pressure regulation problems.