Why Does Brake Fluid Contain Water?
3 Answers
Because the brake pipe connections may not be tightly sealed, driving through water on rainy days can easily lead to water entering the pipes. Here are some key points about brake fluid: 1. Brake fluid is highly hygroscopic. If the water content in the brake fluid is too high, it will lower the boiling point of the brake fluid. Over time, a large number of bubbles will form in the brake lines, significantly affecting the performance of the braking system. When the brake system operates, it generates high temperatures, causing the water in the brake fluid to vaporize. This gas is easily compressed, leading to dangerous situations such as soft brakes, reduced braking power, or even brake failure. 2. During routine maintenance, you can use a brake fluid water content tester to determine if the brake fluid needs to be replaced. New brake fluid typically has a water content of about 0%, and the standard should not exceed 2.5%. If the water content exceeds 2.5%, it is necessary to replace the brake fluid.
Having driven for over a decade, I know that brake fluid absorbing water is quite common. Brake fluid itself is hygroscopic, just like a sponge soaking up moisture—over time, it absorbs water from the air. My old car recently had spongy brakes, and a test revealed excessive water content in the fluid. There are several reasons for this: first, the reservoir cap wasn’t sealed tightly, allowing humid air to seep in; second, after years of use, the brake system’s seals aged and developed leaks; third, summer humidity accelerates water absorption. Water lowers the fluid’s boiling point, risking brake failure if overheated—a serious hazard. That’s why I insist on replacing the fluid every two years, checking the reservoir cap and pipe seals each time to prevent moisture buildup and ensure safe driving. In rainy or humid areas, frequent checks are even more crucial—prevention is always better than dealing with a crisis. During maintenance, a quick water-content test saves a lot of hassle.
As someone who frequently helps car owners with repairs, I've encountered numerous cases of brake fluid contamination by water. The core issue lies in brake fluid being designed hygroscopic to buffer hydraulic pressure, but it absorbs moisture from the air. Common causes during maintenance include: first, owners neglecting regular fluid changes, leading to excessive water absorption over time; second, accidental exposure to humidity when adding new fluid or using unclean tools that introduce moisture; third, system wear causing loose pipe connections that allow rainwater infiltration. Water lowers the fluid's boiling point, potentially causing brake failure during emergency stops and increasing accident risks. I recommend using specialized tools to test moisture content, promptly replacing the fluid and reinforcing seals, typically every 2-3 years, especially for older vehicles and new driving conditions. Preventing this issue ensures both safety and cost savings.
