🔍 Key Concepts

• Difference in viscosity and temperature between residual fuel (HFO) and distillate fuel (MDO/MGO) • Effects of rapid temperature change on fuel system components (pumps, injectors, heaters) • Engine and maker’s recommendations for maximum allowable temperature change rate

💭 Think About

• Think about what happens to pumps, injectors, and fuel pipes if the fuel temperature (and viscosity) changes too quickly. • Is the key concern the total time of the whole changeover, or how fast the temperature of the fuel going to the engine is allowed to change? • Which choice best protects the engine and fuel system from thermal shock and loss of proper atomization at the injectors?

✅ Before You Answer

• Identify which options talk about rate of temperature change versus total elapsed time. • Consider normal fuel temperature differences between heavy fuel oil and marine diesel oil during changeover. • Ask yourself which guideline would be most consistent with a cautious, controlled change that avoids thermal shock and maintains proper viscosity.