Which part of the cooling system stores excess coolant and reduces pressure fluctuations?

• A. Radiator
• B. Water Pump
• C. Expansion Tank
• D. Thermo Switch

Answer: (C)

Cooling systems need somewhere to hold extra coolant when things heat up, and to release it back as things cool down so pressure stays inside safe limits. The expansion tank serves this exact role. As the engine heats, coolant expands and a portion flows into the expansion tank, keeping the radiator and hoses from experiencing excessive pressure. When the engine cools, coolant is drawn back from the tank into the radiator, helping to prevent air pockets and maintaining the correct coolant level in the system. This storage and rebalance smooths pressure fluctuations and keeps the system stable.

The radiator is the heat exchanger, not a storage reservoir. The water pump circulates coolant, but doesn’t absorb excess fluid or damp pressure swings. The thermo switch simply controls when cooling fans run based on temperature, not fluid storage.