WhoCanFixMyCar discusses what brake fluid does, how often it needs replacing and how to go about changing it yourself.
It’s easy to forget that your car's braking system relies on hydraulic fluid that works behind the scenes to amplify the force of your foot on the pedal. This brake fluid doesn't need replacing as often as engine oil, but it's worth familiarising yourself with how to do it.
This guide covers everything you need to know.
What is brake fluid?
Brake fluid is a hydraulic liquid that amplifies your car's braking force and acts as a lubricant. Most modern brake fluids are glycol-ether based, although silicone-based fluids are also available.
Glycol-based fluids are usually used in vehicles with anti-lock braking systems (ABS), whereas silicone-based fluids can only work in cars without ABS technology.
What does brake fluid do?
Most cars on the road today operate using hydraulic brake systems. A simplified explanation goes like this: when you push the brake pedal down, you act on the brake fluid, forcing the pads onto the discs.
Brake fluid is hygroscopic, which means that it likes to absorb moisture. The more moisture it absorbs, the lower the boiling point, making it less effective over time.
Here's how brake fluid works in more detail.
You push the brake pedal. As a result, the pistons in the master cylinder compress, allowing the brake fluid to travel under pressure.
The pistons' compression increases the pressure in the brake lines where the fluid is contained.
Then, the brake lines divert the force of you pressing the pedal into your car's brakes using the fluid.
The fluid converts your energy into braking pressure, causing the pads to squeeze the discs.
Finally, the car slows down.
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 light yellow, almost like vegetable oil, though some variations are slightly different.
The fluid reservoir will depict minimum and maximum fill levels; your fluid should sit between the two. If it's too low, top it up with the correct brake fluid for your car.
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, you’ll need to locate the brake master cylinder and remove the cap. Use a syringe to remove as much 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 on axle stands.
Step two: Fill it back up
Take a lint-free cloth and remove any dirt or debris in the reservoir. Next, fill the master cylinder to the maximum 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 callipers
At the back of each calliper, you’ll find a bleed nipple. Release this to let the old fluid out, starting with the rear wheel on the passenger side. Use a small amount of rubber hose attached to the bleed nipple to 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 right to the floor - use a brick or wooden block to prevent this from happening.
Close the nipple again while the pedal goes back up. This is to avoid letting air into the system.
When the pedal is pressed down, the fluid should escape along with little bubbles. Keep going until you see the new fluid coming through without any bubbles.
Step five: Top-ups
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 calliper. 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 brake fluid do I need for my car?
Different brake fluid types are available; you’ll need to consult your owner’s manual to find the best one for your car.
Dot 3 Brake Fluid
This fluid is primarily found in mass-produced cars because it has the lowest dry and wet boiling points, making it best for everyday use.
Dot 4 Brake Fluid
Dot 4 fluid is very similar to Dot 3, except its additives increase the minimum dry and wet boiling points. It absorbs more moisture than Dot 3 and will need changing more often.
Dot 5 Brake Fluid
This is the only silicone-based brake fluid and cannot, under any circumstances, be used in cars that require Dot 3, 4, or 5.1. It has performance-enhancing qualities and is much 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 with anti-lock brakes.
How often to change brake fluid
Most manufacturers recommend changing 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.
How much does it cost to change brake fluid
The average cost for a brake fluid change is £58.21, according to WhoCanFixMyCar's data.
Frequently asked questions
How much brake fluid do I need?
You shouldn't need more than a litre for a complete brake fluid change, 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 if you decide to top it up yourself.
Is power steering fluid the same as brake fluid?
In a word, no. Brake and power steering fluids are not the same because they are designed for different purposes.
How long does it take to change brake fluid?
If your brake fluid is changed by a professional, this usually will take at most 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 or you simply don't have time, you can use WhoCanFixMyCar to find a local mechanic to do the job for you.
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