How to Choose the Correct Brake Fluid


Perhaps one of the most ignored aspects of our vehicles is the brake fluid.

If the brakes are functioning well, why should we be concerned? However, it plays a key function by transferring foot pressure to the brakes or hydraulic clutch system, while being frequently disregarded. The importance of proper care and maintenance for our automobiles is comparable to that of any other fluid we use. When it comes to braking fluid, there are typically two primary concerns: what should the boiling point be? What liquids are compatible?

How to Choose the Correct Brake Fluid

What Does Brake Fluid Consist Of?

In terms of chemistry, the majority of brake fluid is comprised of various types of glycols, which are essentially a blend of non-petroleum and alcohol-based fluids. Following a blending procedure, the chemical’s name is reduced to “polyglycol.” In addition, there are high-quality silicone-based fluids that cannot be used with other fluid types. Therefore, it is essential to grasp the distinctions between these popular types of brake fluid, regardless of whether they are utilized in the brake or clutch system.

The brake fluid must retain certain characteristics. Our brakes can reach temperatures of up to 1200 degrees Fahrenheit, so the fluid must have a high boiling point. Also, because our vehicles endure the same seasons as we do, they must have a low freezing point. In addition to preserving both extremes, it is meant to protect all rubber brake system components.

Brake fluid characteristics

Consequently, the chemical characteristics present in the majority of braking fluids can permanently dull or harm paint. Therefore, handle with caution and promptly wipe out any unintentional spills. The brake fluid is hygroscopic, meaning it has a natural propensity to absorb moisture. And over time, the extra moisture might cause corrosion or a drop in the boiling point. It is always a good idea to change your brake fluid every couple of years and to avoid leaving the reservoir lid off for longer than necessary.


The most prevalent type of braking fluid used in domestic automobiles and trucks is DOT 3. The Society of Automotive Engineers (SAE) reports that DOT 3 can absorb 2% of its volume in water per year. Over time, excessive moisture will corrode the braking system, leading to problems such as vapor-lock and a mushy pedal.


DOT 4 is designed for use in all types of automobiles, has a greater boiling point than DOT 3, and does not absorb water as quickly. DOT 4 and DOT 3 are compatible, although DOT 3 fluid should not be added to a DOT 4 system. It is the fluid of preference for street and high-performance applications. Almost all of the braking fluids offered by Afco, Wilwood, and Ultra-Lite meet or exceed DOT 4 standards.


Because DOT 5 is silicone-based, it does not absorb moisture. Many street rodders prefer synthetic brake fluid because it is not corrosive to paint or other braking components, making it ideal for conserving antique automobiles for extended periods. However, silicon-based fluids have a few disadvantages: they expand faster when compressed, making the pedal feel spongy, and DOT 5 fluids cannot be blended with other types of braking fluid. DOT 5 fluids typically have a violet hue to distinguish them from DOT 3, DOT 4, and DOT 5.1 fluids.

DOT 5.1

DOT 5.1 is a non-silicone polyglycol with a boiling point greater than 500 degrees. DOT 5.1, unlike DOT 5, is compatible with DOT 3 and DOT 4. In addition, DOT 5.1 typically has the highest rated boiling point, making it ideal for heavy-duty and high-performance applications. The Ultra HTX exceeds DOT 5.1 criteria with a boiling temperature of over 600 degrees.