How often should the brake fluid in a car be changed?
4 Answers
Brake fluid in a car should be changed every 40,000 kilometers or every 3 years. Brake fluid, also known as hydraulic brake fluid, is a functional liquid that transmits pressure in the vehicle's braking system, enabling the braking action on the wheels. Brake fluid does not undergo chemical reactions, is unaffected by high temperatures, and does not corrode, soften, or expand metals and rubber. If brake fluid is not changed for a long time, it can lead to reduced braking force, causing air resistance in the brake lines, which affects braking performance. It can also corrode the brake lines, damage the internal valves of the anti-lock braking hydraulic assembly, and cause wear to the pistons and rubber cups in the brake master cylinder, resulting in contaminated brake fluid.
Last time I got my car serviced, I specifically asked about this. Nowadays, most manufacturers recommend changing the brake fluid every two years or 40,000 kilometers, which makes perfect sense. My car went three years without a change, and once during emergency braking, I felt the pedal go soft. A test revealed the water content exceeded the limit. The mechanic used a testing pen and explained that when moisture exceeds 3%, it lowers the boiling point, potentially causing vapor lock and brake failure under high temperatures. I suggest checking the water content during routine maintenance like I did – in humid southern regions, you might even need to change it earlier. By the way, records show that after changing my brake fluid, my braking distance improved by 1.2 meters per 100 km. When it comes to safety, you really can't afford to cut corners.
Last time I helped my neighbor check her car, I found she hadn't changed the brake fluid for five years. The fluid in the reservoir was turbid and layered. Brake fluid is highly hygroscopic, and factors like aging rubber hoses leaking water or high air humidity can cause moisture infiltration. When brake fluid's water content exceeds standards, its boiling point drops from 260°C to 150°C, potentially causing sudden brake failure during continuous downhill driving. Here's a self-check method: If the brake pedal feels softer than usual when cold, or if there's a burnt smell from the rear, be alert. We veteran mechanics fear these hidden killers the most. It's recommended to change the brake fluid every two and a half years or after long trips like driving the Sichuan-Tibet route.
Having just studied the principle of brake fluid, it is essentially a hydraulic transmission medium. Over time, it not only absorbs moisture but also corrodes metal components, leading to caliper seizure. The manufacturer's manual specifies a theoretical shelf life of 24 months for DOT4 type, but actual conditions depend on the driving environment. Based on my experience, in dry northern regions, it can last up to three years at most, while in rainy southern areas, it's best to replace it every two years. Last time, I used a moisture test strip to check and found that cars parked in garages had 15% lower moisture content than those parked outdoors—parking environment is also crucial.
