What is the standard for brake fluid replacement?
2 Answers
There is no fixed replacement standard for brake fluid. Usually, the moisture content of the brake fluid is used as the basis for replacement, as moisture can lower the boiling point of the brake fluid, causing vapor to form in the brake lines during braking, ultimately leading to ineffective pedal travel and making the brake pedal feel soft, which affects braking performance. Most manufacturers recommend replacing the brake fluid every two years or 40,000 kilometers, although this standard is somewhat conservative. Here is additional information: 1. The reason for the two-year or 40,000-kilometer replacement interval: Manufacturers recommend replacing brake fluid at these intervals as a general guideline because they cannot accurately monitor the actual condition of the brake fluid in every vehicle sold. For example, some vehicles are used frequently, experience heavy braking loads, or operate in humid environments, while others are used less, have lighter braking loads, or operate in dry conditions. To find a balanced approach, the two-year or 40,000-kilometer replacement recommendation was established. If the vehicle is mainly used for daily commuting with little aggressive driving, there is no need to follow the manufacturer's recommendation strictly; simply refer to the moisture content. 2. Brake fluid replacement standard: When the moisture content of the brake fluid reaches 3.5%, it can be replaced. Of course, if the driving environment is only congested urban roads, delaying the replacement slightly is acceptable. In congested urban areas with low average speeds, frequent braking does not generate much heat, so replacement can be done when the moisture content is within 4%.
I've noticed many car owners are confused about when to replace brake fluid. The key factor is its water content. Brake fluid is highly hygroscopic, and as it absorbs moisture over time, its boiling point decreases. When you brake continuously and the fluid temperature rises, it can easily boil, forming bubbles and making the brakes feel spongy and weak. I generally recommend checking it every two years or 40,000 kilometers. You can use a test pen to measure the water content by inserting it into the brake fluid reservoir—if it exceeds 3%, replace it immediately. Don’t just rely on mileage; if you frequently drive on mountain roads or brake aggressively, you might need to replace it every year and a half. When replacing, always go to a professional shop to ensure all air is properly bled from the system. If air bubbles remain, the brake pedal may feel soft, compromising safety.
