Cooling mediumAlthough we call it water cooling, the cooling medium is not pure water, but a mixture of water, antifreeze and various special purpose preservatives, also known as coolant. The antifreeze content of these coolants accounts for 30% ~ 50%, which improves the freezing point of the liquid and prevents the engine from being damaged by freezing at low temperature. The whole cooling system is not connected with the atmosphere, which is equivalent to the role of pressure cooker, and the water tank cover is equivalent to the high-pressure valve. Generally, the allowable working temperature of car coolant can reach 120 ℃, which improves the heat transfer efficiency