Is Brake Fluid Universal?
2 Answers
Automotive brake fluid can also be referred to as hydraulic brake fluid. Brake fluid is not universal, and different models cannot be used interchangeably. Below is the relevant introduction: Reason: You must use brake fluid that matches the original vehicle model. This is because the working pressure of a car's braking system is generally 2MPa, and can reach as high as 4~5MPa. All liquids have the characteristic of being incompressible. In a sealed container or a pipeline filled with liquid, when the liquid is subjected to pressure, it quickly and uniformly transmits the pressure to all parts of the liquid. Characteristics of qualified brake fluid: It ensures flexible transmission of braking force under various working conditions such as high temperature, extreme cold, high speed, and humidity; It is non-corrosive to both metal and non-metal materials in the braking system; It effectively lubricates the moving parts of the braking system, extending the service life of brake calipers and rubber cups.
Brake fluid is indeed not universal, as there are significant chemical differences between various types. My research in this field shows that common types like DOT3, DOT4, and DOT5.1 are glycol-based and can be slightly compatible with each other, but DOT5 is silicone-based and absolutely cannot be mixed. Mixing them can cause the fluid to thicken or form precipitates, clogging the brake lines and leading to sluggish braking response. Even worse, their water absorption properties differ—DOT3 and DOT4 easily absorb moisture, lowering the boiling point and affecting braking performance, while DOT5 doesn't absorb water, leading to separation if mixed with moisture. In short, always check your vehicle's manual and use only the specified type of brake fluid to avoid high risks. Regular fluid changes are also crucial, with a recommended moisture content check every two years.