What are the components of brake fluid?
4 Answers
There are three types of brake fluid: 1. Castor oil-alcohol type, which is made by blending 45% to 55% refined castor oil with 55% to 45% low-carbon alcohol (ethanol or butanol); 2. Synthetic type, which is made by mixing ethers, alcohols, esters, etc., with additives such as lubricants, antioxidants, rust inhibitors, and anti-rubber swelling agents; 3. Mineral oil type, which is made by adding thickeners and other additives to refined light diesel oil fractions. After being used for a certain period, brake fluid is prone to a decrease in boiling point, contamination, and varying degrees of oxidation and deterioration. Therefore, vehicles should regularly check the quality and performance of brake fluid based on climate, environmental conditions, seasonal changes, and working conditions, and replace it promptly. Under normal use, brake fluid should be replaced every 50,000 kilometers or two years.
As someone passionate about automotive technology, I believe understanding brake fluid composition is quite important. Common types like DOT 3 and DOT 4 brake fluids primarily use glycol ether or polyglycol compounds as base fluids, which are highly hygroscopic. Without additives, they easily absorb moisture from the air, leading to reduced boiling points. Additives include corrosion inhibitors to protect metal components in the braking system from rust, antioxidants to prevent fluid degradation, and some friction reducers to minimize wear on pumps and valves. High-performance brake fluids like DOT 4 often incorporate borate esters to enhance wet boiling points, ensuring the fluid doesn't boil and fail during braking. For DOT 5 or 5.1 fluids, silicone-based formulations may replace glycol-based ones—they absorb less moisture but cost significantly more. I always remind myself to change the fluid regularly since component aging affects the entire braking system's reliability and driving safety. When selecting brake fluid, always refer to the vehicle manual's recommendations and avoid mixing different types, as incompatible compositions can cause deposits that clog the lines. In short, a conscientious car owner should understand these core elements.
From a safety perspective, as an ordinary car owner, I'm most concerned about how brake fluid composition affects driving. It primarily consists of glycol ethers or polyglycol compounds, along with anti-corrosion additives like silicates or borates, which help reduce system rust and increase boiling points. These components keep the fluid stable under high temperatures, but once moisture is absorbed, the boiling point drops sharply, potentially causing vaporization and failure during braking. When changing the fluid, I pay special attention to additive quality—premium brake fluids contain more antioxidants to extend lifespan and prevent acidic corrosion from aging. Choosing different DOT grades, such as polyglycol-based DOT 4 over DOT 3, offers higher efficiency, boiling points, and safety. Never opt for cheap, low-quality fluid—impure ingredients accelerate system wear. I replace mine every two years and notice sharper, more reliable braking afterward. Remember: though small, these components are lifesaving essentials.
As a pragmatist, I know from years of driving that brake fluid composition isn't complex. It's primarily based on glycol or polyglycol compounds, with additives including rust inhibitors and stabilizers to protect the system. Different DOT ratings have varying compositions - DOT 3 contains glycol ethers which absorb moisture easily, DOT 4 has higher polyethylene glycol polymerization with better boiling points, while DOT 5 is silicone-based (non-hygroscopic) but prone to air bubbles. Always follow your vehicle's recommended specification, as incompatible formulations can damage brakes. For novice owners, I recommend DOT 4 high-performance fluid for its more comprehensive additive package. Replacement is straightforward and should be done regularly.
