Question 361Motor Plants - Assistant Engineer

The correct answer is C) allow for an increase in water volume as the engine warms up. The expansion tank in a diesel engine's closed cooling system is designed to accommodate the increase in water volume as the engine heats up and the coolant expands. As the engine warms, the water in the cooling system will expand, and the expansion tank provides the necessary space to accept this additional volume, maintaining a constant head (pressure) in the system. The other answer choices are incorrect because: A) an air-cushion is not the primary function of the expansion tank, B) reducing water turbulence is not the main purpose, and D) reducing water temperature is not the role of the expansion tank, as that is the function of the radiator or heat exchanger.