Why is the radiator cap important?

• A. It seals the radiator hose connection.
• B. It filters coolant.
• C. It monitors coolant temperature.
• D. It maintains the system's pressure, raises boiling point, and allows coolant to flow to overflow reservoir when pressure is high.

Answer: (D)

The radiator cap acts as a pressure seal for the cooling system. By keeping the system under the correct pressure, it raises the boiling point of the coolant, which helps prevent boiling over as the engine heats up. The cap also has a valve that vents excess pressure to the overflow reservoir when the coolant expands. As the engine cools, the system draws coolant back from the overflow into the radiator, helping maintain the proper coolant level and reducing air pockets. A faulty cap can lead to loss of pressure, overheating, and coolant loss. It isn’t filtering coolant or directly measuring temperature.