What does DOT4 mean?
2 Answers
DOT4 is a type of brake fluid, typically ester-based. Below is an introduction to DOT4: 1. Composition: The ester type is based on the glycol ether type with the addition of a large amount of borate ester. Borate ester is formed through the esterification reaction of low-polyethylene glycol or propylene glycol with boric acid. Borate ester has a higher boiling point than low-polyethylene glycol or propylene glycol, resulting in better braking performance. Borate ester also has strong moisture resistance, as it can decompose the absorbed water, thereby slowing down the decrease in boiling point caused by water absorption. Therefore, the performance of the ester type is better than that of the glycol ether type, and its price is also higher. 2. Function: Since brake fluid is alcohol-based, it has strong hygroscopicity. Over time, the water content gradually increases. After about 12 months of use, the average water content in DOT4 brake fluid can reach 3%. When the brake fluid contains a higher amount of water, it can cause delayed braking and extended stopping distances. Therefore, it is recommended to replace the brake fluid every 2 years (or 40,000 kilometers).
When it comes to car maintenance, Dot 4 is a specification classification for brake fluid. I always pay attention to it while driving because it relates to critical safety performance. Simply put, Dot 4 indicates a higher boiling point for the brake fluid, typically above 230°C for dry boiling point and above 150°C for wet boiling point, allowing it to withstand high-temperature conditions and prevent bubble formation during frequent braking, which could lead to brake failure. My car’s manual specifically recommends using Dot 4—it’s not something to swap arbitrarily. Choosing the wrong type, like Dot 3, may result in insufficient boiling points, increasing risks on mountain roads or during high-speed driving. Regular replacement is crucial, usually every two years or every 15,000 kilometers, to keep the system fresh. During routine maintenance, I often use a test pen to check the fluid level, ensuring there’s no contamination or water absorption. In daily driving, never overlook this small detail—it ensures more responsive and reliable braking.
