Automotive expansion tank is an important component of the engine cooling system. It serves the main purpose of regulating the temperature of the engine and preventing it from becoming too hot or too cold.

In the case of excessive engine temperature, antifreeze will flow into the expansion tank via the water tank cover to cool down the engine. When the temperature drops to a certain level, the cooling system will suck the antifreeze from the expansion tank into the cooling system via the water tank cover, thus maintaining sufficient coolant in the system.

Methods for determining an expansion tank failure:

1. Check if the expansion tank has water leakage: If water stain or log is discovered on the expansion tank, water may have leaked.

2. Inspect appearance of the expansion tank: If the expansion tank shows obvious deformation, crack, or damage, a failure has occurred.

3. Observe reading of the water temperature indicator: If the water temperature indicator shows an abnormally high reading, it may be due to a failure of the expansion tank that has caused malfunction of the cooling system.

4. Check the amount of remaining coolant in the expansion tank: If the coolant in the expansion tank is insufficient, it may be due to water leakage of the expansion tank.

5. Check whether the automotive cooling system is working properly: If any abnormal condition is found in the cooling system, it may be due to a failure of the expansion tank that prevents the cooling system from working properly.