What Happens if You Overfill Brake Fluid in Your Car?

We all know that regular car maintenance is essential for keeping our vehicles running safely and properly. One task that’s often overlooked, however, is checking brake fluid levels.

Brake fluid is the lifeblood of your brakes, and it’s incredibly important to keep this fluid at the correct level in order to ensure safe driving. But what happens if you overfill the brake fluid in your car?

In this article, I will explore the possible consequences of overfilling brake fluid, as well as provide tips on how to avoid such a situation.

What is Brake Fluid?

A brake fluid is a hydraulic fluid designed to apply pressure to the brakes to slow or stop a vehicle.

It is filled through the master cylinder to the calipers. This is done by the master cylinder pushing it through the pipes and hoses to the master cylinder.

With use and aging, brake fluid can become contaminated by moisture and impurities and lose its effectiveness. This is why it is important to check the level of brake fluid in the master cylinder regularly.

How Brake Fluid Helps Your Car?

Brake fluid works in a similar way as hydraulic fluid in the car. It’s a transparent liquid that has a very high boiling point and a high viscosity, about 3 times as vicious as cold molasses.

This means it can take a lot of pressure before it boils and sets off the pressure sensor. Brake fluid works like hydraulic oil in the car, pumping the brake pistons as the brake pedal is pushed.

As you press the brake pedal, the fluid forces out of the master cylinder and pushes the piston in caliper pistons out, which then squeezes the brake pads against the rotor and the car slows down. It’s a very complicated system, but I hope that clears it up a little bit!

Different Types of Brake Fluids

There are four different types of brake fluids. They are:

  • Glycol brake fluid
  • Silicone brake fluid
  • Petroleum brake fluid

DOT 4 brake fluid is the most popular kind of brake fluid. Brake fluids are incompressible liquids that are used to regulate the pressure in the brake fluid circuit and as a lubricant for the brake components.

The fluid gets transmitted to the brakes through flexible rubber hoses. DOT 4 brake fluid has similar properties to mineral oil and that is why it is called a mineral oil brake fluid.

man checking brake fluid

Why Do Brake Fluids Need Changing?

Rotors and pads in your vehicle wear down as you drive, so it’s important to change the brake fluid regularly to maintain maximum stopping power.

Because the brake fluid is a hydraulic fluid, it absorbs moisture from the air. The moisture in the brake fluid must be removed and replaced with fresh fluid on a regular basis.

If the fluid is not replaced on schedule, it becomes contaminated and wears down the braking system.

The reason that this happens is that brake fluid has anti-corrosive protection, but it is absorbed by the system and eventually lost through evaporation over time.

Another reason to change the brake fluid is that over time it will break down. Breaks down brake fluid can be very dangerous as it will not provide a break as needed and could lead to a significant crash.

How Often Should Brake Fluid be Changed?

Brake fluid should be changed at least every two years or every 30,000 miles, whichever is first. Brake fluid is hygroscopic (which means it absorbs moisture from the air).

Over time, the absorbed moisture corrodes the internal mechanism of your brakes. Therefore, it’s important to check and change the brake fluid regularly.

What Happens if You Overfill Brake Fluid in the Car?

Overfilling the brake fluid in the car is never a good idea as it can cause some short-term and long-term effects.

Brake fluid is a must as it removes the heat generated during the braking process and prevents the car from overheating. It also prevents corrosion and stops the corrosion to spread throughout the brake system.

Overfilling your brake fluid in the car can cause the fluid to flow out and put a lot of strain on the hydraulic system of the car and due to the increased hydraulic pressure, it can damage the brake system.

Overfilling the brake fluid can put a lot of strain on the brake system and it can even cause the brake fluid to overflow from the master cylinder into the fluid reservoir.

Overfilling the brake fluid by flushing your brakes can cause the brake fluid to leak from the brake lines and cause the bleeding process to take longer or may not be effective at all.


We hope you enjoyed our blog about what happens if you overfill the brake fluid in the car. We hope that you won’t have to ever experience a brake fluid leak in your car, but if it does happen, you’ll know exactly what to do.