What is the water content of brake fluid?
2 Answers
Under normal circumstances, the water content of 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 reaches 7-8%, the boiling point of the brake fluid will drop by more than 50%. Relevant information about brake fluid is 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 it becomes excessive, the brake fluid must be replaced promptly. Brake fluid itself is hygroscopic, meaning 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.
Having worked on cars for so many years, I know that the moisture content in brake fluid is a critical factor. If it exceeds 3% to 4%, it becomes dangerous because water lowers the boiling point and reduces braking effectiveness. I've tested it myself with a moisture test pen—if the moisture level is too high, the brakes can overheat and form bubbles when applied, making them practically ineffective. This is no small matter. Once, while inspecting a customer's car, I found the moisture content at 5%, which nearly caused an accident. That's why I recommend testing it every six months; a simple moisture test pen costing just a few dozen bucks is enough. If it exceeds the standard, replace the fluid immediately—don’t delay. Rainy seasons or high humidity can make the fluid more prone to absorbing moisture, so pay extra attention during maintenance. This isn’t just a repair issue; it’s a safety baseline. Don’t skimp on this small expense—changing the fluid is quick and easy, taking just 20-30 minutes at a shop, and it prevents major problems. Remember, braking performance is a matter of life and death—never take it lightly.
