Antifreeze — a means of protection against freezing (Audi A4 B6)

The cooling system is filled with a mixture of water, antifreeze and anti-corrosion agent all year round. This prevents rust and corrosion, salt deposits and, in addition, increases the boiling point of the coolant. In the cooling system, due to the expansion of the liquid when heated, excess pressure is created, which also leads to an increase in the boiling point of the coolant. The pressure is limited by a valve located in the cap of the expansion tank, which opens under pressure 1.4–2.0 atm.

For the cooling system to function flawlessly, it is necessary to insure against boiling of the coolant, which can form a vapor lock, as a result of which the circulation of the liquid decreases and engine cooling deteriorates. The boiling temperature must be increased. To do this, the cooling system must always be filled with a mixture of water and the listed additives to it.