What are the types of brake fluid?
4 Answers
Brake fluid, also known as automotive brake fluid, comes in three types: alcohol-based, mineral oil-based, and synthetic. Below is a detailed introduction to brake fluid: Alcohol-based: There are two grades: No. 1 and No. 3. Mineral oil-based: There are two grades: No. 10 and No. 15. Synthetic: Currently, the most widely used is synthetic brake fluid, which is further divided into three main types: glycol-ether-based, ester-based, and silicone-based. However, the most commonly used are glycol-ether-based and ester-based. Function of brake fluid: The role of brake fluid is to transmit braking pressure. High-quality brake fluid ensures both vehicle safety and the personal safety of drivers and passengers in emergency situations.
I remember checking the manual last time when changing brake fluid, and the main types are DOT 3, DOT 4, DOT 5, and DOT 5.1. DOT 3 is the oldest type, cheap but too hygroscopic with a low boiling point. It needs replacement every year or so, otherwise, the brakes feel spongy. Once I delayed it and almost rear-ended someone in city traffic. DOT 4 is more common and safer, with a higher boiling point, suitable for most family cars and can last two years without replacement. DOT 5 is silicone-based and doesn’t absorb water, which is good, but some vehicle systems aren’t compatible, and mixing it with old fluid can cause issues. DOT 5.1 has the highest boiling point, making it more reliable for highway downhill driving, though it’s a bit pricey. Always check the car manual for recommendations when choosing fluid—don’t switch types randomly. Increased water content can drastically lower the boiling point, which is very dangerous. Now I make sure to check it every two years, using a test pen to measure water content and replacing it promptly if it’s too high.
When dealing with vehicle models, I found there are only a few types of brake fluid: DOT 3, DOT 4, DOT 5, and DOT 5.1. DOT 3 has a boiling point of around 205°C, is low-cost but absorbs moisture quickly, leading to a rapid decline in braking performance when aged. DOT 4, with a boiling point above 230°C, is currently the mainstream choice due to its good compatibility, and is recommended for most vehicles. DOT 5, a silicone-based fluid, has a boiling point of 260°C and resists moisture absorption but can conflict with rubber components, making it unsuitable for older vehicles. DOT 5.1 performs more stably under harsh conditions, with a boiling point reaching 270°C. The replacement cycle is generally every two years or 40,000 kilometers. Prolonged neglect can lead to moisture accumulation, lowering the boiling point and causing brake failure. Choosing the right type and avoiding mixing is crucial—for example, mixing DOT 5 with DOT 3 can cause sediment buildup and clog the system. It’s advisable to use specialized tools to test the fluid’s condition to ensure safe driving—don’t skimp on small expenses and risk major issues.
I asked the technician about brake fluid types, and he said the common ones are DOT 3, DOT 4, DOT 5, and DOT 5.1. DOT 3 is often found in older cars and has poor performance. DOT 4 is the most common, and my car uses this type—it's economical and practical. DOT 5 is silicone-based and doesn't absorb water easily, but some car models don't support it. DOT 5.1 has a high boiling point for safety. Always check the manual when choosing fluid; using the wrong type can affect the system. Mixing different fluids can cause failure—a friend of mine switched types randomly and ended up with abnormal brakes, costing a lot to fix. Regular maintenance and fluid changes can prevent issues. High water content lowers the boiling point, which is dangerous. Generally, changing it every two years is sufficient.
