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A man looking under the bonnet of a car

Drive

How to check and top up brake fluid

Published Nov 2024

3 min read

Text size

Published Nov 2024

Text size

4 November 2024

Brake fluid is a critical part of the hydraulic braking system in your car. When you put your foot on the brake, the fluid is put under pressure, which applies the force that enables your brake pads to grip the brake rotors.

The fluid’s job is to exert high pressure on the brake pads to ensure they grip the rotors with enough force that it slows or stops your car, depending on how much pressure you apply to the brake.

The fluid, along with the brake booster, works to amplify the force of your foot on the brake pedal – without them, you wouldn’t be able to stop your car.

Unscrewing the cap on a brake fluid reservoir

You should check your brake fluid as often as you check your engine oil. To do this, put your car on level ground, then open the bonnet and look for the brake fluid reservoir. This is usually an opaque plastic container with a cap, generally found towards the back of the engine bay. If you’re not exactly sure how to identify it, check the owner’s manual for your car.

There will be a fluid level indicator on the side of the reservoir with a high and low mark. Ideally it should sit close to the high level mark. A low brake fluid level may also indicate a leak, which is another reason why you should check the level regularly.

A brake fluid reservoir showing the high and low fill levels

If the brake fluid reservoir eventually runs out, air can enter the braking system, and this can dangerously compromise braking.

The type of brake fluid you use is important, so check your owner’s manual. Before you top it up, make sure you’re wearing gloves as brake fluid is very toxic. Use a small funnel and place an old rag around the reservoir to protect the surrounding area from any spillages.

Brake fluid acts as a paint stripper, so it’s important to keep it off any painted surfaces.

Remove the filler cap from the top of the reservoir and pour in new fluid until you see it reach the maximum fill line. Make sure you don’t overfill it – this could cause it to squirt out of the small hole in the top of the cap. Replace the filler cap and you’re done.

A close up of brake fluid being poured into a brake fluid reservoir

If you have a manual car with a hydraulic clutch, now would be a good time to also check the clutch fluid, which uses the same stuff.

If you do keep brake fluid at home, make sure it’s kept locked up in secure place. The fluid has a sweet taste so should be kept away from children and pets.

As with your engine oil, over time brake fluid can become contaminated so ideally, every two years the old fluid should be flushed out and replaced. Your mechanic will know when it’s time and do this for you as part of regular servicing.

RELATED:

  • How to check your car's oil level »

  • How to change your windscreen wiper blades »

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