Question 499Motor Plants - Assistant Engineer

The correct answer is B) The temperature of the fuel from the preheater should be gradually reduced after switching over the three-way valve. When switching from heavy fuel oil to diesel oil in a dual fuel main propulsion diesel engine, the temperature of the fuel from the preheater needs to be gradually reduced. This is because diesel oil has a lower viscosity than heavy fuel oil, and a sudden change in temperature could cause issues with the fuel system. Gradually reducing the temperature allows the system to transition smoothly and avoid any potential problems. The other options are incorrect because they do not properly address the need to manage the temperature change when switching fuel types.