Brake fluid — description and safety precautions (Audi A4 B6)

The main components of brake fluid are glycol and polyglycol. This mixture remains fluid even at -40°C, it begins to boil only at a temperature of 270°C. However, being hygroscopic, brake fluid absorbs water (through loose brake hoses and rubber seals). Because of this, the boiling point is lowered - with a water content of 2.5% it is already only 150°C. In this case, when the brakes are strongly heated (driving on mountain roads, full braking) air bubbles can form in the brake fluid. These bubbles are compressed during braking, as a result the system is unable to create stable pressure, the brake pedal is pressed too far (in extreme cases, right up to the floor). For this reason, for your own safety, change your brake fluid regularly, it should be changed every two years, preferably in the spring.

Be careful when handling brake fluid! Brake fluid is poisonous and should not be put into the mouth or on open wounds. Brake fluid does not corrode metal or rubber parts, but it is aggressive to car paint. Fluid drained from the system cannot be reused. Fluid that has been stored in an open container for a long time should also not be used. Used brake fluid is classified as special waste, so make sure it is properly disposed of.

(The text is based on materials from the website: AUDIMANUAL.RU)