Stop Right There: Understanding the Importance of Brake Fluid

February 12th, 2021 by

A mechanic is shown removing the brake fluid reservoir cap on a vehicle

According to Sir Isaac Newton, an object in motion stays in motion… until the driver hits the brakes. Whether you’re the type to stop on a dime or come to a slow and gentle halt, you’re well aware of how important brakes are when driving any type of automobile. You likely take your vehicle in for regular brake service to have all of the components of your brake system inspected, repaired, and replaced as necessary. But many of us aren’t as familiar with the components that make our cars stop as we are with the technology that makes them go.

The parts are smaller and generally hidden from the casual observer. Nonetheless, brakes are an absolutely essential part of any automobile. One aspect that often escapes attention until the situation has become critical is brake fluid. Understanding what brake fluid is and how it impacts the performance of your vehicle is an important part of taking good care of your car, truck, or SUV, which will help it last longer with safer performance.

What Is Brake Fluid, and What Does It Do?

The process of operating your brakes may seem pretty simple. You push the brake pedal. That action compresses a piston inside the brake caliper, which in turn increases the pressure inside the brake lines, sending brake fluid to the rotors. The increased pressure on the rotors causes them to squeeze together onto the brake pads. The brake pads have contact with the wheels, and as those rotors squeeze, the pads gradually slow and stop wheel rotation.

As you may have guessed from the description of the process, your brakes are operating under high pressure and high temperatures, much like your engine. And just like your engine needs lubrication to stay cool and keep all the components moving correctly in that hot and pressure-filled environment, so do your brakes. Brakes need a hard-working fluid that won’t get stuck, won’t build up, and will move exactly when it should to keep your vehicle working safely.

Brake fluid is often called “hydraulic fluid” because of its function in delivering pressure from one mechanical apparatus to another. Without brake fluid, pushing on the brake pedal would have no impact on the rotors and brake pads. This liquid delivers that message through the level of pressure built up in the rotors. But brake fluid does even more than that.

The mechanical process involved in hitting the brakes generates a lot of friction, which creates a lot of heat. Heat leads to moisture condensing in the hydraulic system of your brakes, which can impact performance and lead to damage. Brake fluid absorbs the moisture, preventing it from causing boiling damage and corrosion. It’s designed to handle extreme heat and cold so that you don’t have to worry about brake performance in various types of weather.

A close up shows a mechanic bleeding the brake fluid during a brake service.

Understanding Different Types of Brake Fluid

Just as there are many types of automobiles, there are various types of brake fluid. It’s important to know what type of brake fluid your vehicle requires to ensure that all of the mechanical processes work correctly every single time. There are two main types of brake fluid: glycol based and silicone based.

Glycol based brake fluids are designed for vehicles with anti-lock brake systems, which covers most of the modern vehicles on the road today. Silicone based brake fluids are very specific and only work in vehicles without anti-lock brakes. In fact, if a vehicle has at any time had a glycol based fluid in the brake system, silicone cannot be used. That’s because any trace amounts of glycol left behind will alter the chemical composition of the silicone based fluid.

Brake fluid performance is actually regulated by the United States Department of Transportation National Highway Traffic Safety Administration due to its high level of importance in the operation of automobiles. Each brake fluid is classified by a Department of Transportation (DOT) number, which refers to its boiling point. The most commonly used brake fluids range from DOT 3 through DOT 5.1.

DOT 3 is the most popular and longest-used type of brake fluid. Characterized by a light amber color, it has a boiling point of 401 Fahrenheit when it’s fresh. After extended use, that point drops to 284 F. DOT 3 is highly corrosive and absorbs moisture so that exposure to the air will cause it to degrade.

DOT 4 is common in vehicles from European manufacturers, such as Mercedes, Volvo, and BMW. There are subtypes of DOT 4, such as DOT 4 Plus, DOT 4 Low Viscosity, and DOT 4 Racing. Each version has a different boiling point, starting at 446 F, giving it a higher performance level than DOT 3. The additives in each sub-type of DOT 4 can help reduce acids in absorbed moisture and can change the overall color of the fluid, as well. One rule of thumb is that while DOT 4 can be used in a vehicle that requires DOT 3, the reverse is not true. Vehicles that require DOT 4 cannot use DOT 3.

DOT 5 differs from 3 and 4 in that it is a silicone based brake fluid. It’s usually a purple hue, with an incredibly boiling point of 500 F. Unlike the glycol based fluids, it processes moisture with a bit of foam or air bubbles, making it very difficult to bleed out of anti-lock brake systems. It cannot be mixed with any other fluid and is typically up to 4 times more expensive than the basic DOT 3.

DOT 5.1, however, is glycol based, which is evident from its amber tone. It is similar to DOT 4 Racing brake fluid in performance and boiling point. DOT 5.1 costs up to 14 times more than DOT 3, which means it’s not something you would typically put in your daily driver… unless you professionally race cars.

A close up shows gloved hands removing a caliper during a brake service.

Why Understanding Brake Fluid Is Important to Your Car

If your vehicle is low or running on aged brake fluid, braking will become very difficult. You might find it taking longer to stop or a “squishy” feeling when you step on the brake pedal. Since stopping a moving vehicle is vitally important, so is understanding and paying attention to your brake fluid.

Brake fluid does need to be replaced, but generally not as often as other fluids, like oil. Most experts recommend bleeding and replacing brake fluid every one to two years. However, driving behaviors such as heavy braking or environmental factors such as very high or low temperatures where you typically drive can require more frequent replacement. Always consult your owner’s manual for the recommended brake fluid service schedule, and never hesitate to take your car in for brake service if you find your brakes are not as responsive as they once were.

As brake fluid absorbs moisture, it will become acidic and degrade. This lowers the boiling point, which can compromise the functionality of your brake system. If a quick peek into your car’s brake fluid reservoir reveals a dark fluid, it’s likely time for brake service.

Brake fluid can also be depleted over time, especially as brake components start to run down. A leak anywhere in the system can also reduce hydraulic pressure and cause you to lose brake fluid. Normal wear and tear is expected and can be caused by damage in an accident or when hitting an object with your car, like a curb. Periodically check the brake fluid reservoir to make sure it’s at the “Full” level. If it’s below the “Add” line, then you know it’s time to have your brake fluid and brake system checked and serviced.

Is it Time for You to Get a Brake Service?

Without brake fluid, you wouldn’t be able to stop your car safely and efficiently. Since brakes are an essential part of every vehicle, it’s important to know how to keep them functioning properly at all times. Brake fluid is an absolute must for vehicles; therefore, it’s a good idea for every driver to understand what type of brake fluid their vehicle requires and to look for signs of trouble that may indicate brake service is necessary.

If you think it’s time to get a brake service done, bring your vehicle to Romeoville Toyota. Our service team will be able to check all components of your brakes and brake fluid to ensure that your braking system is working properly. Schedule a service to have your brakes inspected or repaired and your brake fluid changed. Schedule a service online or visit our service center at 684 S. Webster Road in Romeoville today.

Posted in Brake Service