Reserve tank

A reserve tank is a tank that is connected to the radiator cap via an overflow pipe.
When the coolant temperature increases, coolant (water vapor) that flows out from the radiator cap is sent to the reserve tank, and when the coolant temperature decreases, the coolant in the reserve tank returns to the radiator.
The reserve tank works to prevent such wasteful outflows of coolant and enables coolant to be used for long periods of time without needing to be replenished.

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