Brake Fluid

This yellowish fluid is toxic and aggressive toward automotive paint. It does not attack rubber or metal parts. It remains sufficiently fluid even at -40°C, and its boiling point is 260°C, despite the fluid's fluidity.

However, brake fluid has another very unpleasant property: it readily absorbs water, it is "hygroscopic". Water can enter the brake fluid, for example through air humidity via the expansion reservoir, as well as through microscopic leaks at brake hoses and rubber seals. Complete absorption of water, however, does not cause corrosion of the metal parts of the system, but it does cause a significant reduction in the boiling point. With only 2.5% water content, the boiling point is already only 150°C.

This is dangerous under heavy braking, because in this case the brakes become very hot. Near hot brakes, air bubbles can form in the brake fluid. Since air is compressible, the brake pedal will sink to the floor! In this case, only quick pumping of the brake pedal can help. This effect is especially dangerous when braking the vehicle after heavy brake loading. Due to the lack of airflow, brake components heat up even more; the highest temperature is reached approximately 15 minutes after stopping. Only after half an hour does the brake fluid temperature drop back to normal. Therefore, the maintenance schedule prescribes preventive replacement of the brake fluid every two years.

Brake fluid must meet the FMVSS 116 DOT 4 standard. All fluids marked this way may be mixed with one another without concern.