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When you step on the brakes, your car slows and stops as friction material presses against your vehicle’s brake rotors or drums. Behind the scenes, you don’t see the hydraulic operation that centers around brake fluid. Like any other fluid in your vehicle, it needs to be maintained, whether that means topping up low fluid or exchanging dirty, contaminated fluid in the system. A small 12-oz bottle could be under $5 or so, and you can even buy it by the gallon. If you’re having a shop flush the brake fluid, it’s probably in the $100 range. 

What color is brake fluid, and what is it all about? How do you know when it needs to be changed? This article will help you get the answers you need and how best to service your brake fluid

What Is Brake Fluid? 

Brake fluid is a hydraulic fluid. When you press down on the brake pedal, it transfers that force to the calipers or wheel cylinders. That movement creates pressure in the brake lines, and that’s what moves the pistons. The pistons push the pads or shoes against the rotors or drums to create friction and stop your car. It’s a non-compressible fluid, which is why it’s so effective in the brake system.  

Brake fluid also has another important job. It lubricates and protects the parts of your braking system from corrosion. It’s known as a hygroscopic fluid, which means that it traps moisture molecules so they can’t corrode parts internally like the brake lines and calipers, which could cause an unexpected brake problem down the line. 

What Does Brake Fluid Look Like? 

Brake fluid is usually a clear, amber, bluish, red, or greenish color when it comes out of the container and it’s new in the system. You can see it in the transparent reservoir in your engine compartment where you add brake fluid. 

But brake fluid can also be brown or black. And that’s not good. Black brake fluid means it’s time to change it. When the brake fluid darkens, it’s a sign that there are contaminants in the system, whether that’s moisture, dirt, or particles that have worn off the inside of components during use.  

Different Types of Brake Fluid 

There are two main types of brake fluid: DOT 3 and DOT 4. They’re both glycol-based fluids, but DOT 3 has a lower boiling point than DOT 4. That means it breaks down faster and needs to be changed more often – every 20,000 miles or so. DOT 4 can last up to 60,000 miles before it needs to be replaced. 

There are also DOT 5 and DOT 5.1 fluids available. DOT 5 is silicone-based and typically used only for classic cars and other niche applications. DOT 5.1 has a much higher boiling point of around 500F and it’s compatible with both DOT 3 and DOT 4 fluids, where all other types should not be interchanged. Like other car fluid colors, brake fluid specs determine how it appears when new. 

  • DOT 3 fluid might appear as a faint yellow, blue, red, or green shade. 
  • DOT 4 fluid is mostly clear but could have a tinge of yellow or deep red. 
  • DOT 5 often appears purple. 
  • DOT 5.1 brake fluid could be yellow, blue, or crystal clear. 

How to Check Your Brake Fluid 

How to check and top off your brake fluid

It’s easy to check your brake fluid level and condition. Just open the hood and find the transparent reservoir. The level of brake fluid should be between the “min” and “max” lines on the side of the reservoir. If it’s below the “min” line, you need to add more brake fluid.  

If the fluid is a darker color than honey brown, it’s getting old or contaminated, and flushing it out should be on your radar. You can also rub a drop of brake fluid between your fingers. If it feels at all gritty, there’s a problem and it needs to be changed before it causes a failure inside. 

How to Change Your Brake Fluid 

Changing your brake fluid is a little more complicated than checking it. You’ll need some tools, including a socket wrench set, a brake bleeder kit, a lint-free cloth, and a funnel. You’ll also need fresh DOT 3 or DOT 4 brake fluid. The right match can be determined by checking the spec on the reservoir cap, usually. 

Start by opening the hood and finding the master cylinder under the hood. It’ll be close to the firewall and will have a “min” and “max” line on the side. Next, remove the cap from the reservoir and suck the old fluid out, then add clean fluid with a funnel. Put a lint-free cloth over the opening to keep dirt out.  

At each wheel, locate the small bleeder screw. Attach a hose from the brake bleeder kit and open it until the brake fluid starts coming out. Keep it flowing until clean fluid comes out into the hose, then close the bleeder screw. Repeat at all four wheels, topping up the reservoir along the way to prevent air from entering the lines. 

Then, when you’re done, use the funnel to add brake fluid until it reaches the “max” line.  

Now you know all about brake fluid – what color is it, what it does, and how to check and change it. Keep an eye on that brake fluid level and change it when it starts to look black. Your brakes will thank you! 

You can buy your brake fluid at AutoZone to top up or flush the brake system, no matter what spec you need. If you decide that it’s too big a job to tackle on your own, let AutoZone help you find qualified professional mechanics through our Shop Referral Program.  

FAQ/People Also Ask 

What color is brake fluid when it needs changed?

When brake fluid is dark brown or black, it’s time to flush it from the complete brake system.

Is brake fluid black?

When it’s new, brake fluid is always transparent and often has a barely noticeable tinge of color. Brake fluid can be black in the vehicle, but that signifies it’s time to change it.

How do I know if my brake fluid is bad?

Without getting a fluid analysis done, you can tell brake fluid is bad if it’s dark brown or black, milky, or has particulate matter in it.

Does brake fluid look like water?

Visually, clean brake fluid often looks like water but feels oily between your fingers.

Is brake fluid supposed to be brown?

A light honey brown color is usually still in good condition. Dark brown brake fluid can occur in normal circumstances but should be replaced.

Why is brake fluid dark?

Brake fluid gets dark from contaminants that bind to the fluid’s molecules. It can be moisture, shavings from inside the system, or other particles that shouldn’t be present in the fluid.

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