The arrows indicate the "max" (1) and "min" (2) marks on the expansion tank with coolant. For additional monitoring, a control sensor (3) of the coolant level is allowed from below, which signals on the instrument panel with the help of a control lamp or the Auto-Check system about a sharply dropped coolant level.
Using a frost resistance tester (arrow), the concentration of antifreeze is checked.
If the expansion tank cap has to be opened when the engine is hot, there is a high risk of burns - so proceed with caution.
Using a gloved hand or a rag, slowly open the cap one turn and allow the increased pressure to escape from the system. Only then unscrew the cap completely.
If you add only distilled water, you will gradually dilute the coolant, so if possible, you should immediately add a little concentrated antifreeze.
Do not add more than the "max" mark (see previous section); the coolant expands when heated and the excess evaporates from the system.
You can add a small amount of liquid to the expansion tank both when the engine is cold and when it is warm.
If there is significant fluid loss and the engine is hot, do not add cold water to the expansion tank. The "cold shock" may cause the cylinder head to become deformed or the cylinder block to crack.
Coolant
The cooling system does not circulate pure water, but a mixture of antifreeze, including additives that protect against freezing and corrosion, and distilled water. Therefore, it is better to talk about a cooling liquid or a cooling agent. The mixing ratio is 2:3 for European conditions, 1:1 for northern countries.
Just as important as freeze protection is corrosion protection. It prevents scale, rust and other corrosion products from forming in the cooling system. Therefore, the coolant with corrosion protection poured in the workshop should not be drained in the spring, but should be left in the cooling system all year round.
Audi workshops use their own antifreeze agent "G 11 V8 B". The manufacturer also permits the use of other brands bearing the designation "according to TL VW774 B".
[Content source: the specified website: AUDIMANUAL]