Brake Fluid

What Is Brake Fluid? Everything You Need To Know

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Your hydraulic braking system depends on brake fluid, but what exactly is it and what does it do? Do you need to replace or replace bad brake fluid? Below you’ll find the solutions, along with suggestions on when to change your brake fluid and four warning signs that indicate a low level of brake fluid.

What Is Brake Fluid?

In brake systems, brake fluid, a type of hydraulic fluid, helps the brake pedal move so that the brake pads on the wheels can be activated, stopping your car. In addition to being a lubricant and anti-corrosion fluid, brake fluid ensures that the brake system in your car operates at peak efficiency.

What Activates Brake Fluid?

So what precisely happens when you press the brake pedal? First, a vacuum booster located behind the pedal increases the force from your foot. This increased force engages the master cylinder, which then forces pressurized brake fluid into the brake lines. The fluid becomes more pressurized as you apply more force to the brake pedal, increasing the stopping force that is applied by the brakes.

The brake fluid then travels through the brake lines and eventually reaches each wheel’s caliper (or wheel cylinder for drum brakes). At that point, the pressurized fluid propels a set of pistons to push the brake pads up against the rotating rotor. This works because liquid, including brake fluid, is incompressible, or can behave as a solid force even though it moves as a liquid under pressure. The friction that results from the brake pads rubbing against the rotor slows and eventually stops the wheels.

It’s impressive how quickly everything happens. However, if your brake fluid has gone bad or is too low, your brakes won’t be as responsive or, worse yet, they might not work at all. Determining the condition of your brake fluid on a regular basis is essential.

Does Brake Fluid Need To Be Changed Or Is It Going Bad?

Yes, to sum up the answer. As stated in your owner’s manual or as advised by a technician based on the results of a copper level test, brake fluid does eventually go bad and needs to be replaced.

Your brake fluid degrades over time for a few different reasons. The first is that brake fluid readily absorbs moisture from the air because it is hygroscopic, a fancy word for this property. Although your brakes are meant to be a closed system, it is impossible to prevent very small amounts of moisture from interacting with your brake fluid. The brake fluid cap being left open for an extended period of time or microscopic holes in rubber hoses or seals are the usual causes of this.

Your brake fluid’s water content may rise with time if it is exposed to the air. Since water lowers the boiling point of your brake fluid, even a small amount of water contamination can make your brakes less effective.

Corrosion in the brake lines is another factor that could indicate that it’s time to replace your brake fluid. Antioxidants and corrosion inhibitors found in brake fluid help keep crucial brake system components functioning properly. But as time passes, these inhibitors degrade, causing metal corrosion and the accumulation of impurities that obstruct the flow of brake fluid. Additional moisture can also cause metal components to corrode.

Visit your neighborhood car care professionals for a free brake inspection, which includes testing the brake fluid, to avoid driving around with contaminated brake fluid! Depending on their findings, our qualified technicians might advise a brake fluid exchange, which entails draining and refilling the brake fluid in your hydraulic braking system. For more specific advice on brake fluid maintenance, always refer to your owner’s manual.

What Kinds Of Brake Fluid Do You Have?

There are several types of brake fluid: DOTs 3, 4, 5, and 5.1 are examples. The most popular fluids for use in contemporary vehicles are glycol-based DOT 3, DOT 4, and DOT 5.1. DOT 5 is a silicone-based brake fluid that is typically used in vintage cars and other vehicles that require non-petroleum-based brake fluids. It does not absorb water.

In order to prevent corrosion, rust, or general wear, additives are frequently incorporated into brake fluid. Some additives also serve as pH balancers or acid neutralizers.

Which Kind Of Brake Fluid Does My Car Require?

The best way to figure out what type of brake fluid you need for your car is by referring to the car’s owner manual provided by the manufacturer or the master cylinder reservoir cap.

How Often Should I Change My Brake Fluid?

Your car’s owner manual will also specify what kind of brake fluid you need and how frequently you should flush and replace it. In general, brake fluids flushes are recommended every 30,000 miles or two years.

At the end of the day, the frequency of your brake fluid changes depends on your driving habits and braking patterns. Increased mileage, sudden braking, and stop-and-go traffic can all contribute to the need for brake fluid service sooner rather than later.  

Brake Fluid

Signs Of Low Brake Fluid

Soft Pedal

You might be low on brake fluid if your brake pedal feels “softer” than usual or sinks almost to the floor. The brake pedal becomes “squishy” and requires more force from your foot to properly pressurize when there is less brake fluid to compress. Your brakes need to be serviced as soon as possible because this indicates they are not functioning properly.

Abs Warning Light

Your brake fluid may be low if the ABS warning light on your dashboard is illuminated. For the Anti-Lock Brake System to operate properly, the brake fluid levels must be adequate. You might have a leak if the light flashes on and off continuously as you drive. However, if the Service Brakes warning light is on, you might be dealing with something more serious. Every time a dashboard light or warning message appears on your car, it is best to have a professional inspection performed.

Oily Puddle Under The Car

Your brake system may be leaking if you see a pool of liquid accumulating underneath your car that feels slightly oily to the touch. Rubber hoses, the area around the calipers, and the master cylinder are just a few of the places where brake fluid can leak. To ensure your safety, leaks in the brake fluid should be fixed right away.

Old Brake Pads

Brake pads lose thickness over time and need to be pushed farther against the rotor as a result. More brake fluid is required to fill the calipers and squeeze the brake pads the thinner the brake pads are. It’s a good idea to have your brakes serviced, and while you’re at it, consider replacing your brake fluid if your brake pads haven’t been serviced in a while or are whining (possibly an indication that they need to be replaced).

What Are The Most Regular Brake Fluid Problems?

Brake fluid issues historically resulted from moisture leaking into the fluid, but service problems with fluid today differ from those of 20–30 years ago. The majority of problems related to brake fluid moisture intrusion have been solved by modern techniques used to build flexible brake hoses, so moisture in brake fluid isn’t really much of a service issue anymore.

It is now possible to test brake fluid accurately to determine when it needs to be replaced. This is due to the fact that the most frequent problems are caused by the depleted additive package and high levels of dissolved copper in modern brake fluids. Brake fluid’s additive package health can be determined by the amount of dissolved copper present in the fluid. Internal brake system component corrosion and or sludge buildup may occur when the additive package of brake fluid is depleted.

How Do I Check My Brake Fluid?

It’s very easy and practically anywhere to check your brake fluid. Keep in mind that brake fluid is toxic and needs to be handled carefully.

To check the brake fluid in your car, follow these easy steps:

  1. The brake master cylinder is where you should look. The brake fluid reservoir is typically a plain plastic container located on the driver’s side of the car, up against the firewall.
  2. Examine the reservoir’s side and note the fluid level in relation to the fill line to determine the level of the fluid. If your vehicle is older, you will need to remove the metal cap, paying special attention to not letting any type of debris fall in. Once the reservoir is opened, take note of the line that has been marked inside.
  3. If the fluid level is low, you can temporarily alleviate the problem and prevent further harm to your system by adding brake fluid to the entire line.
  4. Close the hood after replacing the cap or top.

It’s crucial to remember that any kind of drop in the brake fluid in your car typically means that your brake system needs maintenance or that there might be a leak in your line. In either case, you should get your car and brakes checked as soon as possible.


For the safety of both you and your vehicle, brake fluid is crucial! It’s best to check your brake fluid to make sure it isn’t preventing you from maintaining your safe driving practices. Visit your neighborhood Tires Plus for a free brake inspection! With no obligations, our mechanics will examine your brake fluid and other crucial brake system parts and offer recommendations based on what they find.

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