Why Does Brake Fluid Decrease in Cars?
2 Answers
There are two main phenomena that cause brake fluid to decrease. First, brake pad wear leads to brake fluid replenishing the pipelines, resulting in a drop in fluid level. Second, there may be leaks in the brake fluid pipelines, so timely inspection and repair are recommended. Below is a detailed introduction to brake fluid: 1. Automotive brake fluid is the liquid used in hydraulic braking systems. It must not undergo chemical reactions, be unaffected by high temperatures, and should not cause corrosion, softening, or swelling to metals and rubber. Currently, DOT3, DOT4, and DOT5 are the commonly used types. 2. Automotive brake fluid has a very low freezing point, ensuring good fluidity at low temperatures. It also has an extremely high boiling point, preventing vapor lock at high temperatures. When used, automotive brake fluid does not cause corrosion to metals or rubber.
After driving for over 20 years, I've found it's quite common for brake fluid to decrease, mainly due to normal consumption from brake pad wear. Every time you press the brake, the piston pushes the pads, wearing them down slightly, and the hydraulic system uses a bit of fluid. Over time, the fluid level naturally drops. But if it drops too quickly or too much, that's a serious problem—usually caused by system leaks, such as aging or cracked seals in the brake calipers, loose or corroded brake line fittings, or fluid dripping out. A small amount may also evaporate in hot weather, but that has minimal impact. Ignoring this issue is dangerous: if the fluid drops below the minimum level, air can enter the system, making the brakes feel spongy or even fail entirely. By the time something happens on a steep hill, it's too late. I make it a habit to check the fluid reservoir monthly—just unscrew the cap to check the level—and if anything seems off, I take it in for repairs immediately. Prevention is key. Checking the brake lines when replacing pads can save a lot of trouble, because safe driving always comes first.
