At What Moisture Content Should Brake Fluid Be Replaced?

[Tate]

Brake fluid must be replaced when its moisture content exceeds 2.5%. Testing Standards: Generally, moisture content is measured using a brake fluid tester, which works by detecting the conductivity of the brake fluid. The results are displayed via built-in light-emitting diodes (indicators) in the testing device. The standard is as follows: if the moisture content is below 0.5%, the brake fluid is in good condition; if it is between 0.5% and 2.5%, replacement is optional; if it exceeds 2.5%, the brake fluid must be replaced. Precautions for Brake Fluid Replacement: During the replacement process, if air enters the brake lines, the brakes may feel softer after replacement, potentially leading to delayed braking or even brake failure. To avoid this, the brake fluid can be replaced using a thorough bleeding method. Open the bleeder valve of the brake caliper, start the engine, and repeatedly press the brake pedal. Once no more fluid comes out of the bleeder valve, tighten it. Refill the master cylinder with new fluid and repeatedly press the brake pedal until it feels firm. Then, loosen the bleeder valve to release fluid, and quickly tighten it when the pedal drops. Repeat this process twice until no air bubbles emerge from the fluid. Always check the fluid level in the master cylinder to ensure it does not drop below the minimum mark.

[Vicki]

When driving long distances, I pay special attention to braking safety. Excessive water content in brake fluid can cause a sharp drop in the boiling point. If it exceeds 3%, it must be replaced because moisture absorbs water, generating vapor at high temperatures that makes the brakes soft and ineffective. I check the water content every six months, which can be easily measured with a specialized tester. Just think about how dangerous brake failure can be in rainy weather or when going downhill. Moreover, water corrodes brake lines, leading to oil leaks. Replacing brake fluid only costs around 100 to 200 yuan, which is much cheaper than major repairs, so if it's found to be excessive, it should be replaced immediately. Regular maintenance can prevent sudden failures and ensure reliable braking every time.

[LaLondyn]

I usually maintain my car myself, and brake fluid is a key inspection item. If the water content exceeds 3%, it must be replaced; otherwise, the boiling point of the brake fluid will decrease, potentially causing bubbles and failure during emergency braking. Moisture is easily absorbed from the air and, over time, can corrode the system. I bought a portable testing tool that checks the color change when a drop of fluid is applied—a red line indicates high water content. It's recommended to replace the fluid every two years, opting for DOT4 type for better high-temperature resistance. When replacing it yourself, ensure all the old fluid is drained and no air enters the lines. Simple maintenance can extend the life of your brakes and prevent issues on the road.

[LaArcher]

Brake fluid absorbing moisture is common, and when the water content is too high, the boiling point can drop to dangerous levels. I recall the standard is to replace it if it exceeds 3%. For example, DOT3's boiling point can drop from 260°C to below 180°C. Moisture also accelerates rusting in metal components, and leakage issues can be a real hassle. I regularly test it myself and address any excess promptly—don't wait until the pedal feels spongy to fix it.