How to Check Brake Fluid

by Contributor

Check the brake fluid when you check all the other fluids. It's easy to do and only takes a minute.

Find the brake master cylinder. This is usually located under the hood on the driver's side of the car, toward the back of the engine compartment. Imagine where your brake pedal would end up if it went all the way through to the engine. The brake master cylinder is a small (about 6-by-2 inches), rectangular piece of metal with a plastic reservoir and a rubber cap on top, and small metal tubes leading from it.

Check your manual if you aren't sure that you've found the master cylinder. The rubber cap will usually read "use only DOT 3 or 4 brake fluid from a sealed container."

Note that on most newer cars the reservoir is translucent and you can see the fluid level without removing the cap. There will be a "full" line, the brake fluid should be at this line.

In older cars (pre-1980) the brake master cylinder reservoir may be made entirely of metal so that you must take the top off to check the fluid level. The top is held on by a metal clamp, use a screwdriver to pop off the clamp and lift the lid.

Add brake fluid to the "full" line. Use the correct brake fluid for your car: Check the rubber cap and your owner's manual to find out what grade of brake fluid your car requires. Most cars use DOT (Department of Transportation) 3 or 4. If the reservoir has 2 parts, fill both halves.


  • check If the brake master cylinder is empty, the brake pedal will go to the floor. If this is the case, you will have to bleed the brakes in addition to adding fluid: Time to see your mechanic, who will flush and refill the braking system.


  • close Brake fluid is very toxic. Keep it away from hands and eyes, and avoid spilling it on the ground. Dispose of empty containers carefully. Be especially careful not to spill brake fluid on your car's paint.
  • close Wash your hands well after handling brake fluid.
  • close Don't drive a car that has run out of brake fluid until bleeding the brakes.

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