NuBrakes Blog Brake Fluid: 4 Signs You Need to Change Your Brake Fluid Image

Brake Fluid: 4 Signs You Need to Change Your Brake Fluid

Brake fluid is a type of hydraulic fluid within a vehicle’s brake and clutch system used to help transfer brake pedal force to stop a vehicle. In other words, when the driver presses on the brake pedal, brake fluid, being incompressible, transfers this pressure to the front and rear brakes and engages the tires to slow or stop the automobile.

Brake Fluid Overview

Brake fluid is integral for the proper functioning of the brake system, allowing proper movement of various components while performing in high temperatures. However, to perform at optimal efficiency, the brake fluid needs to be replaced regularly. As there are many different kinds of brake fluid, make sure to consult the operator’s manual to ensure the proper choice for the vehicle.

To ensure continuing effectiveness, the brake fluid needs tests to identify water and copper content. Electronic monitors and test strips are effective tools to determine whether the fluid is within expected parameters.

Water content inside the brake fluid can be dangerous as it decreases the boiling point while increasing the risk of vapor lock. As a result, the compression of the vapor lock can lead to total hydraulic brake system failure upon the use of the brake pedal. Unfortunately, water also promotes corrosion of important metal brake components.

Corrosion inhibitors in brake fluid degrade over time, which, in conjunction with the presence of excessive water, can cause corrosion in the brake system.

How Does Brake Fluid Work?

When pressure is applied to the brakes, a vacuum booster just behind the pad enhances that force. This boost activates the master cylinder, pushing brake fluid into the lines. The harder the brakes are pressed, the more pressurized fluid becomes, which increases the stopping force.

Brake fluid flows through the lines until it reaches each wheel's caliper or the wheel cylinder. Then, the pressurized fluid forces a set of pistons to push the brake pads against the spinning rotor. Since brake fluid is incompressible, it can act as a solid force under pressure even though it is a liquid. When the brake pads rub against the rotor, the vehicle's friction causes it to slow and eventually stop.

Does Brake Fluid Need to be Changed?

Absolutely. Brake fluids should be changed following the owner’s manual recommendation or that of a qualified technician which is typically every 30,000 miles or every 2 years.

The brake system is designed to be a closed system. However, brake fluid is hygroscopic, which readily absorbs moisture from the air. It is impossible to keep small amounts of water from mixing with the brake fluid, usually due to microscopic holes in rubber hoses, imperfect sealing, or leaving the brake fluid cap open for longer periods than necessary.

Exposure to the air can increase the water content inside the brake fluid. Even a tiny amount of water contamination can cause the brakes to lose effectiveness since water decreases the brake fluid's boiling point. Excess water can also cause metal parts to corrode.

Brake fluid also needs to be changed because there may also be corrosion in the brake lines. Brake fluid has corrosion inhibitors and antioxidants that keep essential parts of the brake system working smoothly, but eventually, these inhibitors break down, leading to metal corrosion and a buildup of contaminants that disrupt the brake fluid flow.

Different Types of Brake Fluid

Understanding the different types of brake fluid can help determine which is appropriate for any given vehicle. The three main types of brake fluid are:

  • DOT3

    DOT3 is one of the most common types as it is an acceptable choice for most vehicles. It has a glycol base and a lower boiling point than other types, with the ability to absorb water from the air.

  • DOT4

    DOT4 brake fluid is similar to DOT3, but its higher boiling point makes it more efficient. Its usage is fairly widespread as well, efficient for many automobile types. DOT4 can withstand a temperature of 230 degrees Celsius, and including additives can reduce moisture buildup inside the system.

  • DOT5

    A silicon-based brake fluid, DOT5 brake fluid can easily sustain temperatures nearing 260 degrees. However, it does not absorb water as well as glycol-based free fluid as it has a higher boiling point, so it is not commonly used for road vehicles.

4 Signs of Low Brake Fluid

It is crucial to keep an eye on brake fluid as it can be dangerous when it runs low. Here are some symptoms that may mean it’s time for replacement:

  • Soft Pedal

    If the brake pedal feels softer than usual or sinks towards the floor without much resistance, this may represent low brake fluid. In this case, the pedal often seems squishy and requires more force from the foot. This is a clear indicator that the brake is not operating effectively and should be serviced soon.

  • Oily Puddle beneath the Vehicle

    If there is a puddle of liquid beneath the car that is slightly oily to the touch, the brake system may be leaking. There are many places where a leak can occur, including rubber hoses, calipers, and master cylinders. If this happens, you should have a professional inspect your braking system immediately to ensure safety.

  • Anti-Lock Braking System Warning Light

    An illuminated anti-lock braking system (ABS) warning light on a dashboard means that the brake fluid is running low and may be indicative of a leak. The ABS needs a sufficient amount of brake fluid level to work correctly, so if the warning light is on, the safest bet is to get a professional inspection.

  • Old Brake Pads

    If the brake pad has not been serviced in a long time or is making a whining noise, it is a good idea to have them serviced and maybe even replace the brake fluid. As brake pads wear down, they become thinner and must be pushed harder for them to reach the rotor. The thinner the brake pads, the more fluid it takes to fill the calipers to properly squeeze them.


Brake fluid is necessary to maintain the vehicle and driver safety. Routine inspections are essential to ensure that there are no mishaps that can lead to injury or even death.

At NuBrakes, we offer a free repair quote and the freedom to select your repair date. Our technicians will check your brake fluid and other essential system components and make recommendations based on what they see.

Contact us to learn more about our service options.


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