Brake fluid

The fluid in brake hoses and brake cylinders is a mixture of glycol, polyglycol ether and a few other elements. This yellowish liquid is poisonous and aggressive towards car paint and will not corrode metal and rubber parts. It itself remains quite fluid at -40°C and, despite its fluidity, has an extremely high boiling point: about 260°C.

But brake fluid has one unpleasant property: it readily absorbs water, it «hygroscopic». Water - for example, due to atmospheric humidity - can actually penetrate into the brake fluid: through the expansion tank or through microscopic leaks in brake hoses or rubber cuffs. Such water absorption leads not only to corrosion of the metal parts of the system, but also causes a rapid decrease in the boiling point of the brake fluid. With a water content of only 2.5%, its boiling point is only at 150°C.

This is dangerous when the brakes are heavily loaded, because. they get very hot at the same time. Vapor bubbles can form in the hydraulic fluid near hot brakes. They are compressed - the brake pedal can sink deep, sometimes the foot just presses into the void! In this case, a quick pumping of fluid with the brake pedal sometimes helps. This effect is especially dangerous when stopping the car after a heavy load on the brakes. Due to the lack of a headwind, everything surrounded by the brakes heats up even more; during parking, the maximum temperature is maintained even after 15 minutes of parking. And after about half an hour, the temperature of the brake fluid drops to normal.

Therefore, the maintenance plan calls for a preventive brake fluid change every two years.

Brake fluid must comply with US FMVSS §571.116 DOT 4 and SAE J 1703. All fluids listed with this designation can be safely mixed. Opel uses ATE and Lockheed brake fluid.