Mahle coolant expansion tank CRT209000S

An expansion tank, also known as a coolant reservoir, is an important component of a car's cooling system. Its primary function is to compensate for changes in the volume of coolant in the system due to temperature fluctuations. As the engine heats up, the coolant expands and the excess is routed to the expansion tank. Likewise, when the engine cools down, the coolant contracts and is drawn back into the radiator from the expansion tank.

Without an expansion tank, the increased pressure from the expanding coolant would put stress on the radiator and could potentially cause it to crack. Additionally, without a reservoir for excess coolant to go into, the system would be more susceptible to air pockets, which can impede the flow of coolant and cause overheating. In short, the expansion tank helps to maintain the proper level of coolant in the system and ensure that the engine stays cool and operating within a safe temperature range.