What are the types of automotive brake fluid?

3 Answers
Lucy
07/24/25 11:54am
There are three types of automotive brake fluid: castor oil alcohol type, synthetic type, and mineral oil type. Brake fluid is the liquid medium that transmits braking pressure in hydraulic braking systems, also known as brake oil or force oil, with the English name Brake Fluid. It is an indispensable part of the braking system, serving as the medium for transmitting force. Since liquids cannot be compressed, the pressure output from the master cylinder is directly transmitted to the wheel cylinders through the brake fluid. The composition and efficacy of different types of brake fluid vary. For example, castor oil alcohol type brake fluid is made by blending refined 45% to 55% castor oil with 45% to 55% low-carbon alcohol, and then precipitating to obtain a colorless or light yellow clear and transparent liquid, known as alcohol-type automotive brake fluid. Castor oil plus ethanol is Alcohol Type 1, while castor oil plus butanol is Alcohol Type 3. Alcohol-type brake fluid is easy to produce with readily available raw materials and simple synthesis processes, and the product has good lubricity. However, it has a low boiling point and unstable properties at low temperatures. Alcohol Type 1 will produce ethanol vapor above 45 degrees, causing vapor lock. At minus 25 degrees, castor oil precipitates as a milky white colloidal substance, which increases as the temperature decreases, clogging the braking system and making it heavy and ineffective.
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ColtonLee
08/11/25 2:55am
Commonly used brake fluids can be chemically categorized into four main types: DOT3, DOT4, DOT5, and DOT5.1. DOT3 is primarily used in older vehicles, with polyethylene glycol as its base material, which tends to corrode components when moisture content is high. Most newer vehicles now use DOT4, which has a higher boiling point, better performance, and typically requires replacement every two years. DOT5 and DOT5.1 are more specialized, with silicone-based compositions that hardly absorb moisture, offering much longer maintenance intervals. However, their viscosity differs, so compatibility with specific vehicle models must be checked. It's crucial not to mix different types during replacement, as this can damage the brake system's seals.
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Ibarra
09/25/25 4:45am
Common brake fluids are classified into four levels according to international standards: DOT3 has strong water absorption and must be replaced every two years; DOT4 is the most widely used, with a dry boiling point exceeding 230°C, making it more suitable for the braking performance requirements of modern vehicles; DOT5 is silicone-based brake fluid, which hardly absorbs water but has slightly poorer compressibility, often used in specific vehicle models; while DOT5.1 combines high boiling point and low viscosity characteristics, mainly suitable for new vehicles equipped with ABS/ESP. When selecting, remember to check the model specified in the vehicle manual, as mixing different types can corrode the brake caliper seals, which requires special attention.
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