This yellowish - and, by the way, poisonous and aggressive towards auto varnish - liquid does not corrode rubber and metal parts. It remains quite fluid even at minus 40°C, and its boiling point is located at 260°C. But brake fluid has another very unpleasant property: it is hygroscopic. Water can actually get into the brake fluid, for example, through air humidity, through the expansion tank, as well as microscopic leaks on the brake hoses and rubber cuffs. Complete absorption of water does not lead to corrosion of the metal parts of the system, but to a strong decrease in the boiling point. With only 2.5% water content, the boiling point is only at 150°C.
This is dangerous when the brakes are heavily loaded, because in this case they get very hot. Air bubbles can form in the working fluid near hot brakes. Since we compress the air, the brake pedal will fall to the floor! In this case, only a quick «pumping up» brake pedal. This effect is especially dangerous when braking the car after a heavy load on the brakes. Due to the lack of oncoming airflow, the brake elements heat up even more; the highest temperature is reached after about 15 minutes of parking. Only after half an hour the temperature of the brake fluid drops back to normal.
Therefore, the maintenance plan proactively calls for changing the brake fluid every two years. Brake fluid must comply with FMVSS116DOT4. All liquids marked in this way can be mixed with one another without fear.
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