Question 312Motor Plants - Assistant Engineer

The correct answer is C) at the main engine fuel oil header. The viscosity of heavy fuel oil will be lowest at the main engine fuel oil header because this is the point where the fuel oil has been heated and conditioned the most. As the fuel oil travels through the system, it is typically heated to reduce its viscosity and improve its flow and atomization properties. The fuel oil will be at its lowest viscosity at the point closest to the main engine, which is the main engine fuel oil header. The other options are incorrect because the viscosity will be higher in the settling tank (A), at the transfer pump discharge (B), and in the three-way valve (D) due to the lower temperature and less conditioning of the fuel oil at these points in the system.