Different Types of Brake Fluid
Brake fluid is the lifeblood of the brake system and a commonly overlooked but integral part of your vehicle. It’s a hydraulic fluid responsible for one job: stopping your vehicle! Brake fluid transfers the action of pushing on the pedal to the brake calipers or drums through a series of brake hoses and lines to actually stop your vehicle. Because it must operate under very demanding conditions without failure, the United States’ regulates the performance qualities of it from the Department of Transportation’s National Highway Traffic Safety Administration. It must pass testing for the ability to remain fluid at a low temperature, resist boiling at a high temperature, compatibility with other brake fluids and parts of the braking system, and controlling the corrosion of your brake system.
Brake fluid is referred by DOT and a number. The DOT stands for Department of Transportation. Each number has a higher boiling point. Most vehicles in the USA take DOT3 or 4 which are amber in color, like a light beer. They are glycol-based and will absorb moisture out of the air (hygroscopic is the science term). Thus, you’ll want to keep the top of your bottle tight and don’t open the master cylinder reservoir unless needed. Most master cylinder reservoirs are clear for this reason. Because of its affinity to absorb moisture and the heat generated during braking, brake fluid performance will degrade over time. It will become acidic, promoting the formation of rust and debris in the system, which can clog valves in an expensive ABS system.
By far, DOT 3 is the most popular. It’s been in use for a very long time. Fresh DOT 3 has a boiling point of 401 degrees Fahrenheit, fully degraded it drops to 284 degrees Fahrenheit. This makes your brake fluid much more likely to boil. Braking hard, going downhill for a long period, towing, or racing can speed up this process.
Since DOT 3 is highly corrosive, great care should be taken. It will remove paint and should be cleaned up immediately using soap and water or a simple degreaser.
DOT 4 is beginning to be used more widely in by vehicle manufacturers, but is used mostly by European car manufacturers currently. Although there are different types of DOT 4 brake fluid, it has a higher boiling point than DOT 3. These boiling points start at 446 degrees Fahrenheit. Additional additives in DOT 4 help reduce the acids that can form from moisture.
While DOT 3 and 4 are technically intermixable, it is not recommended. DOT 4 is twice the cost of DOT 3 and for most, there’s little benefit to switching. There are several different types of DOT 4 so be certain you use the correct type.
DOT 4 is used in some euro and domestic vehicles. DOT 4 Plus is used in Mercedes and Volvo. DOT 4 Low Viscosity is used in some BMW models. Finally, DOT 4 Racing usually has an added blue color.
DOT 5 is a silicone-based brake fluid and has a very high boiling point of 500 degrees Fahrenheit. Usually it has a purple color to differentiate from the amber color of DOT 3 and 4. It doesn’t absorb water quite like the glycol-based brake fluids, but it does become foamy and the air bubbles are far more difficult to bleed out. This is why DOT 5 is not recommended for an ABS systems.
DOT 5 is not able to be mixed with any other fluid, and is 4x more expensive than DOT 3.
DOT 5.1 is a glycol-based brake fluid with a boiling point similar to DOT 4 racing brake fluids. Usually clear to amber in color. While it is technically intermixable with DOT 3 or 4, it is not recommended. DOT 5.1 is around 14x more expensive than DOT 3.
PowerStop components are only compatible with glycol-based DOT 3, 4 ,and 5.1 brake fluids. All brake fluids should be handled with care, though. Take measures to prevent contact with your skin or eyes, and is harmful if swallowed. The bottom line is that all brake fluid ages, which degrades performance. To keep your vehicle’s brake system at peak performance, flush your fluid in accordance with the OEM maintenance schedule and use the factory recommended brake fluid.
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Remember, Don’t Just Stop…PowerStop!