Can DOT3 Brake Fluid Be Replaced with DOT4?
2 Answers
DOT3 brake fluid cannot be replaced with DOT4, as doing so would lower the dry and wet boiling points of the brake fluid. This not only increases the risk of vaporization in the system, leading to vapor lock, which can cause delayed braking or even brake failure, but also affects the stability of the brake fluid. Continuous braking under such conditions poses certain dangers. Brake fluid, also known as brake hydraulic fluid, is made from refined diesel fractions combined with thickeners and antioxidants. There are three types of brake fluid: mineral oil-based, alcohol-based, and synthetic. The typical working pressure for braking systems is around 2MPa, with some reaching up to 4-5MPa.
With years of experience in car repair, I often help customers upgrade from DOT3 to DOT4 brake fluid because DOT4 has a higher boiling point, preventing bubble formation during aggressive driving that could lead to spongy brakes. However, a thorough system flush is essential before the switch—residual DOT3's strong hygroscopic nature can cause component corrosion and leaks if mixed. Always check your vehicle manual for upgrade compatibility; while most modern cars support it, older models might not. The upgrade enhances brake responsiveness, ideal for mountain driving or heavy-load scenarios. After the change, test-drive multiple times to ensure no air is trapped, and regular maintenance is key to prolonging component lifespan.