“Why change my brake fluid every two years?”

From the Globe and Mail, question was "Why change my brake fluid every two years?"

The 48,000-km maintenance schedule recommends to replace the brake fluid. Have you ever heard of this being done on other vehicles? Is it really necessary?

As I understand it, the hydraulic system is a closed system with no way for pollutants or dust to enter unless via the reservoir filler cap. The service adviser also said that the boiling point might change. Huh?


ANSWER: Most car manufacturers recommend changing the brake fluid every two years or so.

Brake fluid is highly susceptible to absorbing moisture. As this happens, it changes the very nature of the fluid, including the boiling point.

The hydraulic brake system is indeed sealed, but moisture can be absorbed through the seals in any system. Over time, this moisture can cause corrosion in the critical and very-expensive-to-replace ABS components.

But it is the change in boiling point that is critical. The minimum boiling point of brake fluid, depending on SAE grade, is in the range of 401 to 446 F. This is necessary because of the tremendous heat created when the pads clamp on the disc or press against a rotating drum when slowing the vehicle.

If the brake fluid reaches the boiling point, vapour bubbles are created. Brake fluid is meant to transfer pressure to the pads, pushing them against the rotors or drums. If there are tiny bubbles in the system, they are compressed when you press on the brakes, and this compression reduces the force transmitted to the brakes.

It only takes a tiny amount of moisture to bring the boiling point below the recommended minimum and, when you need maximum braking in an emergency situation, performance would be reduced.

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