In a diesel engine closed cooling system, the expansion tank is designed to allow expansion of water volume as temperature rises.

In a diesel engine closed cooling system, the expansion tank is designed to allow expansion of water volume as temperature rises.

• A. Allows expansion of water volume as temperature rises
• B. Maintains a constant head on the system
• C. Filters the coolant
• D. Increases system pressure

Answer: (A)

The key idea is that a closed cooling system must accommodate the coolant’s volume increase as it heats. When the engine warms up, water expands, and without space for that extra volume the pressure would rise and could lead to boiling or leaks. The expansion tank provides a reservoir connected to the cooling loop where the expanding coolant can flow and be stored. As the engine cools, the coolant contracts and is drawn back into the system, helping to keep the level balanced and prevent air pockets. This arrangement also helps vent air during filling and operation, but it doesn’t filter the coolant, and it doesn’t set the operating head by itself—the system pressure is governed by the pressure cap and pump. So the expansion tank’s main role is to allow and manage the expansion of water volume with temperature changes.

The key idea is that a closed cooling system must accommodate the coolant’s volume increase as it heats. When the engine warms up, water expands, and without space for that extra volume the pressure would rise and could lead to boiling or leaks. The expansion tank provides a reservoir connected to the cooling loop where the expanding coolant can flow and be stored. As the engine cools, the coolant contracts and is drawn back into the system, helping to keep the level balanced and prevent air pockets. This arrangement also helps vent air during filling and operation, but it doesn’t filter the coolant, and it doesn’t set the operating head by itself—the system pressure is governed by the pressure cap and pump. So the expansion tank’s main role is to allow and manage the expansion of water volume with temperature changes.