PDF download Download Article PDF download Download Article

Your car's brake system is one of several automotive hydraulic systems. When you push down on the brake pedal, fluid is delivered through the brake lines from the master cylinder to the brake drums or discs, slowing the car through friction. To make the system work properly, you need to have enough brake fluid in the system, and it needs to be in good enough condition to do its job.

Get Car Support Solve Any Problem

wH
Hi there! Do you have a question about how to diagnose or fix a problem with your car? I’ve read the manual so you don’t have to. Select your make, model, and year, then ask away!
*
*
Method 1
Method 1 of 2:

Checking the Brake Fluid Level

PDF download Download Article
  1. [1] It's best to do this when the car is stopped on a level surface, with the engine cold.
  2. Watermark wikiHow to Check Brake Fluid
    [2] On most cars, the master cylinder is located at the back of the engine bay, on the driver's side. There's a reservoir above the cylinder itself.
    Advertisement
  3. [3] On most newer cars, the reservoir is transparent, with lines marked "Min" and "Max"; the brake fluid level should fall between these lines. Cars older than the 1980s may have metal reservoirs, requiring you to remove the reservoir cap. (Newer caps screw on and off, while some older caps need to be pried off with a screwdriver.)
  4. Watermark wikiHow to Check Brake Fluid
    Pour the fluid carefully into the reservoir, wiping up any spills, as brake fluid is toxic and corrosive.[4]
    • Use only the brake fluid with the DOT specification recommended in your owner's manual. There are three main specifications: DOT 3, DOT 4 and DOT 5, each having its own properties. It is possible to use DOT 4 brake fluid in some cars that call for DOT 3 fluid, but never the reverse, and DOT 5 brake fluid can be used only in cars that call for that specification. Note that most cars indicate the required brake fluid DOT at the reservoir cap.
    • This is also a good time to check how well the reservoir cap seals.
  5. Watermark wikiHow to Check Brake Fluid
    [5]
    • If the brake fluid level is significantly below the "Min" or "Add" line, you should have your brakes inspected for excessive wear. As brake pads wear down, brake fluid can channel itself out of the brake lines into the calipers.[6]
    • It is also possible to have the brake fluid reservoir full and not have the brake fluid reaching the master cylinder. If your brakes feel spongy even with the reservoir full, take your car to a mechanic.
  6. Advertisement
Method 2
Method 2 of 2:

Checking the Brake Fluid Condition

PDF download Download Article
  1. Normally, brake fluid is brown. If the fluid looks dark or black, it may need to be replaced but further testing is needed.[7]
  2. Watermark wikiHow to Check Brake Fluid
    [8] As brake fluid ages, its corrosion inhibitors break down. Test strips check the presence of copper in the brake fluid; the higher the level, the more worn out the inhibitors are. One such test strip is Phoenix Systems' "Brake Strip Brake Fluid Test Strip"
  3. [9] Brake fluid is hygroscopic, which means that over time, it absorbs moisture from its surroundings. Moisture dilutes and weakens the effectiveness of brake fluid, which leads to braking systems components to corrode. In 18 months, brake fluid can have up to 3 percent water, which can lower its boiling point from 40 to 50 percent.
  4. New DOT 3 specification brake fluid is to have a dry boiling point of 401 degrees Fahrenheit (205 degrees Celsius) and a wet boiling point of 284 degrees (140 degrees Celsius), while DOT 4 fluid is to boil at 446 degrees (230 degrees Celsius) dry and 311 degrees (155 degrees Celsius) wet. The lower the point at which the brake fluid boils, the less effective it is.
    • Your mechanic should have both an optical refractometer and electronic brake fluid tester to perform these tests for you as part of an automotive checkup.
  5. Advertisement

Community Q&A

Search
Add New Question
  • Question
    My brakes don't squeal but my pedal goes to the floor. What is the issue?
    Community Answer
    Community Answer
    You may have bad linkage or the brake fluid may be low on a more modern car.
  • Question
    Should the engine be hot or cold when I'm checking the brake fluid?
    Community Answer
    Community Answer
    It doesn't matter, although you might feel more comfortable if the engine is cold.
  • Question
    What color should the brake fluid be?
    Logic Johnson Lafontaine
    Logic Johnson Lafontaine
    Top Answerer
    If it's new, it can be clear or amber. As it gets older, it will turn closer to brown.
See more answers
Ask a Question
200 characters left
Include your email address to get a message when this question is answered.
Submit
Advertisement

Video

Tips

  • Most manufacturers specify times for when brake fluid should be replaced. Check your owner's manual for information specific to your make and model.
  • One reason your brake fluid may be bad involves moisture. Brake fluid is hygroscopic - this means it absorbs moisture - from the breather hole in the master cylinder reservoir cap, from the rubber hoses, and possibly from the "new" bottle of brake fluid if the cap hasn't been kept on it.
Submit a Tip
All tip submissions are carefully reviewed before being published
Name
Please provide your name and last initial
Thanks for submitting a tip for review!
Advertisement

Warnings

  • In addition to seeing your brake or ABS warning light come on, if your brake pedal feels too hard or spongy, goes down too far, makes noise, drags or pulsates, or if your car pulls to one side or gives off a burning smell while braking, take the car in for servicing.
Advertisement

Things You'll Need

  • Bottle of brake fluid
  • Funnel (optional)
  • Rag or paper towel

You Might Also Like

Flush Power Steering FluidFlush Power Steering Fluid
Add Brake Fluid to the Clutch Master CylinderAdd Brake Fluid to the Clutch Master Cylinder
Electric Parking Brake Problem Diagnose and Fix Problems with Your Electric Parking Brakes
Change a Brake CaliperChange a Brake Caliper
Check Brake Pads Check Your Brake Pads For Wear: Visual Signs & Measurement Tips
Reset Parking Brake Light Fix a Parking Brake Light That Won’t Turn Off
Test a Brake BoosterBad Brake Booster: Symptoms, Tests, and Troubleshooting
Replace a Master CylinderReplace a Master Cylinder
Change The Brake Pads in Your Car
Brakes Locking UpBrakes Locking Up While Driving? Causes & Fixes
Bleed a Master CylinderBleed a Master Cylinder
Adjust Drum BrakesTesting and Adjusting Your Vehicle's Rear Drum Brakes
Replace Brake RotorsAn Expert-Approved Guide to Replacing Brake Rotors Like a Pro
Replace Drum BrakesReplace Drum Brakes
Advertisement
  1. Videos provided by Jon Olson
  2. [1]
  3. [2]

About This Article

Ed Beery
Co-authored by:
Automotive Specialist
This article was co-authored by Ed Beery. Ed Beery is an Automotive Specialist and the Owner of InTechgrity Automotive Excellence based in Denver, Colorado. With more than eight years of experience, he specializes in providing maintenance and repair services for both individuals and companies. Ed and the InTechgrity Automotive Excellence Team are approved by the American Automobile Association (AAA) for repairs and are Automotive Service Excellence (ASE) certified. This article has been viewed 396,755 times.
9 votes - 67%
Co-authors: 14
Updated: March 24, 2024
Views: 396,755
Article SummaryX

To check your vehicle’s brake fluid, start by opening the hood and finding the master cylinder, which is toward the back of the engine bay on the driver’s side. Then, look at the reservoir next to it and check if the fluid falls between the “Min” and “Max” lines on the container. If it’s below the minimum, carefully add more fluid. Also, check the color of the brake fluid to make sure it's brown and not black. If it looks black, you may need to replace it. For tips on how test your brake fluid if you think it needs to be changed, read on!

Did this summary help you?

Thanks to all authors for creating a page that has been read 396,755 times.

Did this article help you?

Advertisement