Why do I need to Check Brake Fluid?

We often forget just how many times we press our brake pedal, even in the shortest of trips. Every time we do, we really on the hyrdaulics of the brake system to assist us in stopping the vehicle. This hydraulic system multiplies the force we can apply through the brake pedal to effectively slow and stop our vehicle.

Your owner's manual will advise you to regularly check and top up the level of brake fluid in your vehicle. This is a good start, but it's very important to also check the condition of your brake fluid as this affects the braking performance of your vehicle. Most brake fluids such as DOT 3 and DOT 4 are hygroscopic - this means they will absorb moisture when exposed to air. Moisture is the main enemy of brake fluid and is most often absorbed through the brake fluid reservoir or brake lines even when the vehicle is not being used.


Moisture in the brake fluid decreases its boiling point which reduces the effectiveness and heightens the risk of a brake failure. Some systems can absorb as much as 2% of moisture for every year the vehicle is in operation. 

During regular driving, the brake pads can reach extremely high temperatures as the friction forces between the brake pads and discs creates heat. This is then transferred into the brake fluid which can raise the fluid temperature to over 200°C. When the fluid gets too hot, small air bubbles start to form as it begins to boil, reducing the effectiveness of the fluid at transferring force since air is more compressible than the surrounding fluid. This increases the risk of greater pedal travel, spongy brake feel and longer stopping distances. 

How to Add Brake Fluid

When you step on your brake pedal, it’s the brake fluid that helps activate your brakes to slow you down. So, brake fluid is important.

Things like brake pads and discs (also called rotors) have visual indications of wear and tear but brake fluid does not and so is often overlooked. But like any fluid in your vehicle, brake fluid needs to be checked regularly and occasionally changed. Taking a look at the brake reservoir every month will tell you if the level is fine or if you need to add fluid.  If your brake fluid looks a little low, here’s how to top it off.

Before You Start

There are a few things you should do before starting:

  • Park your vehicle on a level surface.
  • Use eye and hand protection when you handle brake fluid as it is toxic.
  • Roll up or remove loose clothing, and keep your arms away from the cooling fan(s) — fans can turn on automatically, even when the engine is off.
  • Consult your owner’s manual for the specific type of brake fluid recommended for your vehicle. Only use fluid from a clean, unopened container. Never substitute another fluid for brake fluid.
  • Never let the master cylinder run dry; this could cause brake failure.

Adding Brake Fluid to Your Vehicle

  1. With the engine off, raise the hood and find the brake master cylinder. It is usually in the back of the engine bay, on the driver’s side.
  2. Cover the fender before opening the brake master cylinder and use caution when opening a container of brake fluid as it can damage your vehicle's paint.
  3. Use a cloth or towel to clean the master cylinder’s reservoir and cap to prevent dirt or water from entering while you service it. Clean the fluid lines too, if they need it.
  4. Look at the fluid level on the side of the master cylinder’s reservoir. If your brake fluid is at or above the “MIN” line, your brake fluid level is fine and you don’t need to add any.
  5. If your fluid is below the “MIN” line, carefully pry the reservoir cap off, and then add brake fluid until the level is just under the “MAX” line. Do not overfill.
  6. Using a completely clean towel or a lint-free cloth, clean the inside of the reservoir cap: It may have brake fluid, dirt/debris, or both on it, and needs to be clean before you put it back on.
  7. Carefully set the reservoir cap on the reservoir, and press down on all four corners until it clicks into place.

Visit your local dealership to have your brakes inspected as soon as possible—especially if your fluid level continues to go down, or if your fluid is dark. You may need your brake system serviced. If you are at all unsure about changing the brake fluid go to your local dealership to have a professional do it for you.

Quick Tip

There are three main types of brake fluid: DOT 3, DOT 4, and DOT 5.

DOT 3 and 4 are glycol-based brake fluids and the main difference between them is the boiling point: DOT 4 boils at a higher temperature which can be beneficial if your brakes see very heavy use, or if you participate in motorsports. Of course, you should check your owner’s manual first to make sure DOT 4 can be used in your vehicle.

DOT 5 fluid is silicone-based: It doesn’t absorb moisture like DOT 3 and DOT 4 fluids do, and it has a higher boiling point. However, DOT 5 fluid should never be added to vehicles that specify DOT 3 or 4 fluid as brake system damage can occur.

For vehicle specific information about brake fluid, please see your Owner's manual or contact your local dealership.