What are the symptoms of high water content in brake fluid?
2 Answers
Under normal circumstances, the water content in brake fluid is below 1%. If it is too high, it will lower the boiling point of the brake fluid, causing the brake fluid to boil and vaporize during high-intensity braking, leading to brake failure. When the water content in the brake fluid reaches 3%, the boiling point of the brake fluid will decrease by 25%; if the water content in the brake fluid reaches 7-8%, the boiling point of the brake fluid will decrease by more than 50%. The relevant details about brake fluid are as follows: Introduction to brake fluid: Brake fluid is also known as hydraulic brake fluid. The water content in brake fluid has a certain proportion, and when the water content is excessive, it must be replaced promptly. Brake fluid itself is hygroscopic, and moisture from the air can seep in through the vent hole of the brake fluid reservoir. Over time, this can cause the water content in the brake fluid to exceed the standard. Function of brake fluid: It effectively lubricates the moving parts of the braking system, extending the service life of the brake calipers and rubber cups.
I've been running an auto repair shop for nearly twenty years and have seen plenty of issues with high water content in brake fluid. The most typical symptom is the brake pedal becoming unusually soft and spongy, lacking firmness when pressed, which significantly increases braking distance. Especially during prolonged driving or continuous braking, as the fluid temperature rises, the water content lowers the boiling point, creating air bubbles that block the lines and cause vapor lock, leading to brake failure. Additionally, the calipers and wheel cylinders in the brake system are prone to rust and corrosion, and the ABS function can also be affected. I once had a customer who neglected to change the fluid in time and nearly rear-ended someone on the highway, ending up having to replace the entire brake system at considerable unnecessary expense. I recommend checking the brake fluid's water content every two years or 20,000 kilometers—just use a dedicated test pen to see if moisture levels are excessive. Don't wait until an accident happens to regret it. Regular maintenance saves both peace of mind and safety.
