Which component serves as a reservoir for excess coolant when pressure rises in the cooling system?

Which component serves as a reservoir for excess coolant when pressure rises in the cooling system?

• A. Radiator cap
• B. Coolant reservoir
• C. Expansion tank
• D. Overflow bottle

Answer: (C)

When the engine heats up, the coolant expands and the system must accommodate that extra volume without losing pressure. The component that acts as the main reservoir for this excess coolant is the expansion tank. It sits in the cooling loop, taking in the additional coolant as pressure rises and then returning it to the radiator as the system cools, helping to maintain proper level and prevent air pockets. The overflow bottle is just a catch vessel for coolant that spills out when the system is hot, not the primary reservoir used to manage expansion. The radiator cap helps regulate system pressure, while the term coolant reservoir can refer to the same tank in some vehicles, but the function described—holding the excess coolant during expansion—belongs to the expansion tank.

When the engine heats up, the coolant expands and the system must accommodate that extra volume without losing pressure. The component that acts as the main reservoir for this excess coolant is the expansion tank. It sits in the cooling loop, taking in the additional coolant as pressure rises and then returning it to the radiator as the system cools, helping to maintain proper level and prevent air pockets. The overflow bottle is just a catch vessel for coolant that spills out when the system is hot, not the primary reservoir used to manage expansion. The radiator cap helps regulate system pressure, while the term coolant reservoir can refer to the same tank in some vehicles, but the function described—holding the excess coolant during expansion—belongs to the expansion tank.