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How to check and change brake fluid

Ellie Dyer-Brown, 1 year ago

3 min read

  • Advice
  • Maintenance

WhoCanFixMyCar discusses what brake fluid does, how often it needs replacing and how to go about changing it yourself.

It’s easy to take your brakes for granted. In this guide, we’ll cover what brake fluid is, what it does, why it sometimes needs replacing and how you can change yours at home. 

Guide contents:

How to check brake fluid

How to change brake fluid

What is brake fluid?

What does brake fluid do?

Which brake fluid do I need for my car?

How often to change brake fluid

How much does it cost to change brake fluid?

Frequently asked questions

How to check brake fluid

Follow these steps to check your brake fluid.

  • Take your car on a short drive and brake several times to fill the system with fluid

  • Park somewhere flat

  • Locate the brake fluid reservoir (your owner's manual will tell you where it is)

  • Inspect the fluid level and colour

Your brake fluid should be a light yellow colour, almost like vegetable oil, though some variations are slightly different.

The fluid reservoir will depict a "minimum" and "maximum" fill level; your fluid should sit somewhere between the two. If it's too low then top it up with the correct brake fluid for your car.

Oil-Pouring close up

How to change brake fluid

Here are the basic steps you need to follow to change your brake fluid.

Step one: drain the old fluid

First of all, you’ll need to locate the brake master cylinder and remove the cap. Use a syringe to remove as much of the fluid as possible, storing it in a secure container. 

After this, it’s time to tackle the brakes themselves. The best way to do this is to put your car up on axle stands and remove all the wheels. 

Step two: fill it back up

Take a lint-free cloth and clear out any dirt or debris that is in the reservoir. After this, fill the master cylinder back up to the MAX line with the correct fluid. Make sure you use new fluid from a sealed container, otherwise it could have already absorbed moisture from the air, rendering it useless.

Step three: flush the calipers

At the back of each caliper you’ll find a bleed nipple. Release this to let the old fluid out, then spray it with brake cleaner and penetrating oil to free any remaining fluid up. Drain all of this into the same container you used earlier. 

Step four: ask for help

Now it’s time to find a handy assistant to sit in the driver’s seat and gently press down the brake pedal after you’ve opened the first bleed nipple. Note: the pedal shouldn’t be pressed all the way to the floor. Once the pedal is down, close the nipple again while the pedal goes back up. This is to avoid letting air into the system. 

Each time the pedal is pressed down, fluid should escape along with little bubbles. Keep going until you see the new fluid coming through.

Step five: top ups

You will need to keep topping up the fluid level in the master cylinder as you go through this process. If it gets too low, avoid pumping the brake pedal, as this will result in air getting into the system.

Step six: repeat

Repeat the same process for each caliper. Once you’ve finished, dispose of the old brake fluid sensibly - don’t pour it down the drain! Your local recycling centre is the proper place to take it. 

What is brake fluid?

Brake fluid is a hydraulic liquid that’s used to transfer force into pressure, amplifying the overall braking force. Most modern brake fluids are glycol-ether based, although silicone-based fluids are also available. 

Glycol-based fluids are usually used in vehicles which have anti-lock braking systems (ABS), whereas silicone-based fluids can only work in vehicles that don’t rely on ABS technology.

What does brake fluid do?

Most cars on the road today operate using hydraulic brake systems. This means that when you push the brake pedal down, you act on the brake fluid, which then forces the pads onto the discs. 

Brake fluid is hygroscopic, which means that it likes to absorb moisture. The more moisture that it absorbs, the lower the boiling point becomes, meaning it becomes less and less effective over time. 

Furthermore, if there is a problem with your braking system and the fluid gets too hot, it could start to boil. Air bubbles will form as a result, which is very bad news for hydraulic brakes! Air bubbles allow the brake fluid to be compressed, so it’s no longer able to act on the brakes when you press the pedal. This can happen after periods of prolonged braking or when the car is driven fast on a race track.

What brake fluid do I need for my car?

There are different types of brake fluid available, so in order to find the best one for your car you’ll need to consult your owner’s manual. 

Dot 3 Brake Fluid

This type of fluid is primarily found in mass-produced cars because it has the lowest dry and wet boiling point and is therefore best for everyday use.

Dot 4 Brake Fluid

Dot 4 fluid is very similar to Dot 3, except it has additives that increase the minimum dry and wet boiling points. It absorbs more moisture than Dot 3 and will need changing more often as a result.

Dot 5 Brake Fluid

This is the only silicone-based brake fluid and cannot under any circumstances be used in cars which require Dot 3, 4 or 5.1. It has performance enhancing qualities and subsequently is a lot more expensive than the other fluids.

Dot 5.1 Brake Fluid

Dot 5.1 was created when silicone-based fluid failed to go mainstream. It offers the same performance benefits but can be used in cars that have anti-lock brakes.

How often to change brake fluid

Typically, most manufacturers recommend you should change your brake fluid every two years regardless of your mileage.

Each car is different, so the best thing to do is check your owner’s manual to find out how long your fluid can go before it needs to be replaced.

Looking under car hood image

How much does it cost to change brake fluid

The average cost for a brake fluid change is £68.43 according to WhoCanFixMyCar's data from 2021.

Average cost of a brake fluid change

Frequently asked questions

How much brake fluid do I need?

For a full brake fluid change, you shouldn't need any more than a litre, but your owner's manual will specify the exact amount.

What colour is brake fluid?

Brake fluid is a light golden colour, almost like vegetable oil. If it appears murky or dark you should change it immediately.

Where does brake fluid go?

Brake fluid sits in a reservoir near the master cylinder.

Is brake fluid flammable?

Yes, brake fluid is flammable, harmful, and corrosive, so you should be extremely careful when handling it if you decide to top it up yourself.

Is power steering fluid the same as brake fluid?

In a word: no. Brake fluid and power steering fluid are very different as they both serve different purposes.

How long does it take to change brake fluid?

If you have your brake fluid changed by a professional this usually won't take much more than an hour, but doing the job yourself can take a lot longer, especially if you haven't changed your brake fluid before.

If changing your own brake fluid sounds a bit beyond your capabilities - we wouldn’t blame you! - then you can use WhoCanFixMyCar to find a local mechanic to do the job for you, so you can sit back and relax.

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