🔍 Key Concepts

• Optimal operating temperature range for medium-speed marine diesel engines • How closed treated fresh water cooling systems and expansion tanks affect boiling point and corrosion control • Typical trade-off between efficiency, wear, and coolant life at different jacket water temperatures

💭 Think About

• Which temperature range is warm enough to promote efficient combustion and reduce cylinder wear, but not so hot that it risks boiling or damaging coolant additives? • How does using a treated fresh water closed system allow higher safe temperatures compared with raw seawater cooling? • Think about the usual thermostat setting ranges used in medium-speed marine diesels—where do they typically start opening and become fully open?

✅ Before You Answer

• Eliminate any range that is too low to be realistic for a modern diesel’s normal operating jacket water temperature • Eliminate any range that is so high it would approach or exceed the safe limits for coolant and expansion tank design in a vented system • Consider what range most manuals describe as the normal jacket water outlet temperature for medium-speed engines, not starting/warm-up temperatures or emergency limits