What Is Brake Fluid?

Many different parts contribute to the operation of the brakes in a vehicle. Because the braking system is one of the main safety features of a car, all of its parts should be maintained properly.

Brake fluid, also known as hydraulic fluid, is an essential part of a car's braking system and is necessary for the brakes to function properly. Brake fluid takes the force applied at the brake pedal and translates it into pressure, which is then sent to the brakes to stop the vehicle.

Brake fluid cannot be compressed and operates under high pressure and temperatures. It is important to regularly check the condition of brake fluid and change it as needed to ensure the braking system functions smoothly. There are different types of brake fluid, including DOT 3, DOT 4, DOT 5 and DOT 5.1, each with different characteristics and uses. Brake fluid should be clear and yellowish in color when in good condition. Dark brown or black fluid indicates the need for replacement.

Keep reading to find out why brake fluid is essential to the operation of the braking system.

What Does Brake Fluid Do?

Simply put, a car’s braking system doesn’t work without brake fluid. The brake fluid takes the force from the depressed brake pedal, translates it into pressure and sends this pressure to the front and rear brakes to stop a vehicle.

Brake fluid can’t be compressed, which makes it perfect for use within a hydraulic braking system. It’s able to operate under the high pressure and temperatures generated when a car is coming to a stop. The role that brake fluid plays is relatively simple when broken down:

• The driver steps on the brake pedal.
• The linkage applies force to the piston at the master cylinder.
• The master cylinder pressurizes the brake fluid and sends it toward the wheel cylinders and calipers.
• The hydraulic pressure acts on pistons to produce force.
• The force is exerted on the brake pads, which make contact with the brake drum or rotor.
• Resulting friction causes the rotation of the wheels to slow or stop.

Without brake fluid, there wouldn’t be the pressure necessary to get your vehicle to a safe and complete stop. Any leaks or fluid that hasn’t been changed in a while can cause issues on the road if not addressed.

How Often Should Brake Fluid Be Changed?

You should make sure to check the condition of your brake fluid often and change it on a regular basis to ensure the braking system as a whole is able to run smoothly.

It’s easy to check the condition of brake fluid by looking – a brake fluid reservoir is under the hood and there are markings showing what the appropriate level of fluid should be. Fluid should be added if it’s at a lower level than normal and monitored in case there’s a leak.

A good rule of thumb is to check the brake fluid every time your vehicle gets an oil change. As far as completely replacing the fluid, this time frame can vary depending on the vehicle and driving conditions. Referring to an owner’s manual is the best bet to find the recommended time frame for your specific vehicle.

If your car runs out of brake fluid due to a leak in the system or damage to a part, the brakes are not going to work properly. It’s unsafe to drive with a low amount of brake fluid or a leak in the system.

Signs Your Brake Fluid Is Low

It’s helpful to know the signs and symptoms that might indicate your vehicle has a low amount of brake fluid. These can include:

• The brake light comes on. The anti-lock braking system (ABS) indicator light is designed to illuminate if something within the brake system needs to be checked. This can be a pretty obvious indicator, so be sure to check the fluid levels if you notice this.
• Issues with your brake pedal. You might notice a few things happening with your brake pedal if your car doesn’t have a proper amount of brake fluid. It might be harder to press down on it, or the pedal might have a “soft” feel when you use it.
• Brake pad problems. Your brake fluid works alongside parts of the braking system, including the brake pads. This means that if you hear any loud noises coming from the pads or that they’re not working properly, it could be an issue stemming from lack of brake fluid.
• Burning smells. Any burning smells or smoke coming from your vehicle is never a good sign. This might indicate that your brakes are overheating.
• Odd noises. A lack of brake fluid or brake fluid that is past its prime can cause strange noises from your braking system. These can be scraping or squealing noises.

Be sure to take these symptoms seriously and ensure that you have the right amount of brake fluid in your vehicle. It might be time for a change!

Different Types of Brake Fluid

Knowing what brake fluid does and how it helps with the operation of the system is a good first step as a car owner. It’s just as important to know the difference between kinds of brake fluids, which are known by different Department of Transportation (DOT) numbers.

Brake fluid types include:

• DOT 3: This is one of the most common types of brake fluid. It has a glycol base and the lowest boiling point among the fluids listed here. It also can absorb water from the air. Most vehicles can use DOT 3 brake fluid.
• DOT 4: DOT 4 braking fluid is similar to DOT 3, but with a higher boiling point. This makes it a more efficient fluid. It’s also very common and can be used in a range of vehicles.
• DOT 5: When looking at DOT 3 or DOT 4 versus DOT 5 brake fluid, the biggest difference is that DOT 5 is a silicon-based fluid instead of glycol. It doesn’t absorb water like the others and has the highest boiling point. It’s not commonly used on road vehicles.
• DOT 5.1: This brake fluid is an improved version of DOT 4. It has an even higher boiling point which helps sustain braking efficiency. It’s important to note that this type of brake fluid typically needs to be replaced more often because it absorbs moisture quicker than the other types. 

What Does Brake Fluid Look Like?

Regardless of its DOT number, brake fluid looks the same across the board. New brake fluid or fluid in good condition is clear and might have a yellow tint to it. It should remain relatively clear through routine checks over the years.

Brake fluid in need of replacement will get darker and darker. It generally will resemble motor oil – anything dark brown or black indicates that the fluid should be replaced.

Brake Fluid FAQs

Is brake fluid toxic?

Brake fluid does wonders for your car but is toxic to living organisms. This means that swallowing or skin-to-skin contact with brake fluid could cause irritation, a bad reaction and even be fatal.

How often should brake fluid be changed?

The brake fluid should be changed depending on the manufacturer’s recommendation for your vehicle. So, how long does brake fluid last? A good rule of thumb is to replace your brake fluid every two to three years or every 30,000 – 50,000 miles.

Can I mix different types of brake fluid?

You can mix brake fluids only if you are adding a higher-grade fluid into the system. For example, if the current system has DOT 3 fluid in it, you can add DOT 4 or DOT 5.1 fluid. However, if you have DOT 5.1 fluid in the system, you can only replenish the brake fluid with DOT 5.1 fluid.

DOT 4 and DOT 5.1 fluid can be mixed without causing issues. Always make sure that the brake fluid you’re mixing with DOT 4 is DOT 5.1 and not DOT 5. DOT 4 and DOT 5.1 are glycol-based while DOT 5 is silicon-based, so they are incompatible.

Learn About Braking Systems at UTI

Changing your brake fluid is something that can be done at home, though it’s important to have some basic understanding of cars and to follow vehicle-specific instructions.

If you’re someone interested or passionate about the automotive field and are looking for a new career, then pursuing an education as an automotive technician could be the next best step to take.

In the Automotive Technology program at Universal Technical Institute (UTI), you’ll learn a range of skills that can help you in your day-to-day life and prepare you for a career.¹ There’s an entire course on brake systems that covers all things brake-related, including hydraulic systems and brake fluid.

You can learn more by requesting information online to get in touch with one of our Admissions Representatives, or by calling 1-800-834-7308.

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