Between the engine compartment and the windshield, a reservoir with brake fluid is placed in the so-called moisture box (1), brake master cylinder (2) and brake booster (3). The photo clearly shows the fill level marks of the tank «MAX» And «MIN».
This yellowish liquid, poisonous and aggressive towards car paint, does not corrode metal and rubber parts. It itself remains quite fluid at -40°C and, despite its fluidity, has an extremely high boiling point of about 260°C.
But brake fluid has a very 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 the brake hoses or rubber cuffs. Such water absorption not only causes corrosion of the metal parts of the brake system, but also causes a rapid drop in the boiling point of the brake fluid. With a water content of only 2.5%, its boiling point is only at 150°C. Vapor bubbles can form in the hydraulic fluid near hot brakes. They are compressed - the brake pedal can sink deep, sometimes the foot simply 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 headwind, everything surrounded by brakes heats up even more. 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 FMVSS 116 DOT 4 specification. All fluids with this designation can be safely mixed.
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