Will brake fluid boil if the temperature is too high?
2 Answers
Audi S5 has a displacement of 3.0 liters, equipped with a 3.0L V6 turbocharged engine, delivering a maximum power of 260kW and a maximum torque of 500Nm. The Audi S5 is a coupe under the Audi brand, available in two-door, four-door, and a two-door convertible version. When the driver presses the brake pedal, the master cylinder uses brake fluid to push the slave cylinders, which then press the brake pads against the brake discs, converting kinetic energy into thermal energy and slowing the car down. During the friction between the brake pads and discs, a large amount of heat is generated, which transfers to the pistons in the slave cylinders. These pistons are actuated by brake fluid, and if the temperature becomes too high, the brake fluid can boil.
I often drive on mountain roads, and brake fluid can indeed boil when the temperature gets too high. During continuous hard braking, such as when going down a long slope, the brake disc temperature can soar to 500-600 degrees Celsius, transferring heat to the brake fluid lines and rapidly increasing the fluid temperature. Once it exceeds the boiling point of the fluid (for example, standard DOT3 fluid boils at 205°C), the fluid vaporizes, creating air bubbles. This causes the hydraulic system to fail, making the brake pedal feel soft and unresponsive, which can easily lead to brake failure. I experienced this firsthand once on a mountain road and nearly had an accident. Now, I always use DOT4 or higher-grade fluid with a boiling point above 230°C, and I regularly check the fluid condition. Aged fluid that has absorbed moisture has an even lower boiling point and is more prone to boiling. I've made it a habit to change the brake fluid every two years, reduce continuous braking time on long, steep slopes, and use intermittent braking or engine braking to control speed—safety first.
