Complete Guide To Brake Fluid

Brake fluid is a major component of any car braking system and you’ll want to ensure it’s changed regularly, which is usually every two years. To help increase your knowledge, below is our complete guide regarding brake fluid.

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Brake Fluid Change
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What Does Brake Fluid Do?

The purpose of brake fluid is to transfer hydraulic pressure from the master cylinder to the brake pads. This has the effect of slowing your car down as you press the brake pedal inside of your car.

As you can imagine, if you haven’t used the correct fluid or not enough of it, your brakes won’t work as expected. The quality of the brake fluid you require can be found in your car’s owner’s manual and it will state the fluid by a “Dot” rating, which can include Dot 3, Dot 4 and Dot 5. The same fluid may also be used to operate the clutch, which is the reason why the two fluids can be interchangeable.

How Much Does A Brake Fluid Change Cost?

The cost to replace your brake fluid can vary due to the labour required for specific vehicles and the brake fluid that you intend to use. As a rough approximation, a brake fluid change would cost approximately £40 to £70 for a budget to mid-range cars (i.e. Ford, Volkswagen, Nissan etc). If you drive a premium car such as a Mercedes, BMW or any type of performance/supercar, a brake fluid change may cost anywhere from £100 to £200.

Where Is The Brake Fluid Reservoir

If you need to top up your brake fluid, it’s crucial that you pour the fluid into the correct reservoir. Nine times out of ten, the brake fluid reservoir is located on top of the master cylinder, which will be to the back left or right of your engine.

As you can see in the below photo, the brake fluid reservoir is small in size and has a min/max guideline for filling it up correctly. If you accidentally put too much fluid into the reservoir, use an oil extractor to remove the excess.

Where Is The Brake Fluid Reservoir

How To Change Brake Fluid

If you want to avoid the labour cost of a mechanic, changing your brake fluid yourself is relatively straightforward. It’s advised that you change the brake fluid every two years to ensure the brakes work as they should. The main reason for the two-year guideline is due to the fact that any longer may result in too much water content in the fluid.

In order to change your car’s brake fluid, follow the six steps below:

  1. Purchase the best-rated brake fluid for your car (either dot 3, 4 or 5).
  2. Remove the cap from the reservoir and remove as much fluid as possible.
  3. Use a lint-free cloth to clean any dirt inside the reservoir and fill it back up with new fluid.
  4. Flush each of the calipers via the bleed nipple on the back (use a brake bleeding kit or another person).
  5. Top up the brake fluid in the reservoir when required.
  6. Keep repeating steps 4 and 5 until you have a good “pedal” feel (i.e. firm).

Regarding step 4, you will want to work with a partner in order to depress the brake pedal as you open the bleed nipple. Once they have pressed the brake pedal, you’ll want to tighten the bleed nipple and then tell your partner to release the pedal. Each time the brake pedal is pressed down with the bleed nipple open, a small amount of fluid should come out. You’ll want to carry on doing this process to each of the calipers until no fluid leaves the bleed nipples.

Leaking Brake Fluid

If you suspect that your car is leaking brake fluid, it’s certainly something that you shouldn’t ignore. Eventually, you may begin to notice the brake pedal becoming spongy, which can be a sign that you need to get it sorted out as soon as possible.

Other signs that your brake fluid is leaking include:

  • Dashboard warning light
  • Yellow/brown fluid underneath your car
  • Leaks around the master cylinder

In terms of fixing the leaking brake fluid, you’ll want to inspect the master cylinder, ABS module, brake lines, bleeder valves, rotors, drum, pistons and other brake components. If possible, by using an OBD2 scanner, you may be able to identify the exact cause of the problem and save hours of guesswork. Depending upon the leaking component, you’ll be able to make the necessary repairs in order to stop the leaking brake fluid. Sometimes it can be as simple as the reservoir cap being loose or the bleed nipples not being tightened properly.

Dot 3 vs Dot 4 vs Dot 5

As mentioned briefly above, brake fluid is given various ratings that are “Dot” rated. The three main types include Dot 3, Dot 4 and Dot 5, which are all industry standards among most car manufacturers.

The majority of cars will use either a Dot 3 or Dot 4 brake fluid which are both glycol based. The only difference between the two is the fact that Dot 4 fluids contain more borate ester, which allows it to handle more heat. Dot 5 is less common and is a silicone-based fluid that’s developed for use where moisture or water may be a factor in the braking system.

Depending upon how you intend to use your car (i.e. daily driving, track days, off-roading) should determine which brake fluid you use. However, we strongly recommend sticking to the Dot-rated fluid that’s stated in your owner’s manual.


Although brake fluid isn’t as talked about when compared to engine oil, it’s just as important in terms of your car’s performance. The stopping capabilities of your car shouldn’t be ignored and regular brake fluid changes are highly recommended.

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