Question 1 QMED03 - Oiler

The Correct Answer is D ### Explanation for Option D (Correct Answer) Option D is correct because in most standard marine main diesel engine cooling water system diagrams (like the typical configurations illustrated in diagrams such as MO-0129), the **Lube Oil Cooler (or Main Engine Lube Oil Cooler)** and the **Jacket Water Cooler (or High Temperature [HT] Fresh Water Cooler)** are designed to be connected directly in series on the *freshwater side* (HT circuit). The typical flow is: 1. Engine Jacket Water (HT circuit) leaves the engine cylinder jackets. 2. It flows directly to the **Jacket Water Cooler** where it rejects heat to the Low Temperature (LT) circuit (seawater or LT central cooler circuit). 3. The cooled Jacket Water then flows directly through the **Lube Oil Cooler** to pick up the heat rejected by the main engine lube oil before returning to the engine circulation pumps. Alternatively, some systems place the lube oil cooler first, but they are almost always placed sequentially (in series) within the HT circuit to manage the overall heat balance and maximize cooling efficiency before the jacket water returns to the engine. ### Explanation for Incorrect Options **A) Jacket water cooler and scavenge air cooler(s)** * **Incorrect:** These two components operate in different cooling circuits. The **Jacket Water Cooler** is in the High Temperature (HT) circuit. The **Scavenge Air Cooler(s)** is/are typically cooled by the Low Temperature (LT) circuit (which is often a separate centralized cooler circuit or direct seawater). They are therefore connected in parallel relative to the engine's main cooling requirements, not in series on the same HT line. **B) Camshaft lube oil cooler and jacket water cooler** * **Incorrect:** The **Camshaft Lube Oil Cooler** handles a minor, isolated cooling load. This cooler is almost always connected in parallel with the main HT system flow, often taking cooled jacket water *after* it has exited the main Jacket Water Cooler and returning it directly to the system pump suction or back into the main HT return line, but not directly in series with the main flow path of the Jacket Water Cooler itself. **C) Camshaft lube oil cooler and scavenge air cooler(s)** * **Incorrect:** These two components are cooled by two different circuits (Camshaft Cooler typically by HT or sometimes LT water, and Scavenge Air Cooler always by LT water). They are never connected directly in series with each other.