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Hardly anyone has the brake fluid on their radar. A mistake, because poor maintenance can be dangerous. How often does it need to be changed? And how much does it cost to change the brake fluid? All the info.

Very few drivers bother to change their brake fluid. In principle, they don’t have to, because it is checked and regularly changed as part of the inspection. However, it never hurts to check the expansion tank in the engine compartment, as a leak in the line can also cause a gradual loss of fluid.

Drivers who do not regularly visit the workshop for service – often drivers who do not drive very often or owners of older vehicles – should, however, pay particular attention: the brake fluid must be changed every two years at the latest.

What you didn’t know about your brake system

The brake is one of the most important safety systems on a car. Since the invention of the automobile, it has been the subject of intensive tinkering.

Did you know that:

  • the first vehicle with a brake booster was the Mercedes 300 SL in the 1960s? This reduced the pressure on the brake pedal by around 50 percent.
  • an antilock braking system completes about 10 braking operations per second? On a motorcycle, it’s as many as 15.
  • new brake fluid can reach temperatures of up to 536 degrees Fahrenheit before it reaches its boiling point? However, the more water there is in the fluid (unavoidable over time), the faster it boils and no longer functions properly.

Every braking maneuver creates friction, and where there is friction, there is wear. To ensure your own safety, that of your passengers, and that of other road users, regular maintenance and servicing of the entire braking system is required. This also includes changing the brake fluid. This is something that vehicle owners tend to underestimate. Here you can find out all about why and how often you should have the brake fluid changed and what it costs.

Why do you need brake fluid?

The braking system of a vehicle usually works hydraulically. The brake fluid transfers the pressure exerted by the driver on the brake pedal to the wheel brake.

How often and why does the brake fluid need to be changed?

Regardless of the mileage, the brake fluid should be replaced every two years at the latest. Porous brake hoses, for example, can cause it to absorb water – brake fluid is hygroscopic, meaning it binds moisture.

Why is this so bad? The brake system and fluid can get very hot. So hot that the accumulated water boils and steam bubbles form. In extreme cases, the brake pressure can no longer be applied and the brake fails!

What happens if the brake fluid is too low?

This can also lead to brake failure. The expansion tank in the engine compartment indicates whether there is enough brake fluid. The system holds a total of around two liters.

What are symptoms of low brake fluid?

brake fluid change

How to notice that brake fluid is missing?

If the red warning light in the dashboard with the brake symbol (red exclamation mark in a circle) lights up, caution is required. It indicates either that the handbrake is still applied or that there is a problem with the brake system because the brake fluid has dropped or the pads are worn. Since the brake system is a safety-relevant component, you should stop driving, follow the instructions in the owner’s manual, and, if in doubt, call roadside assistance.

But there are other indications of insufficient brake fluid. Does the braking effect diminish or can the brake pedal be depressed very easily without much resistance? Or is it delayed in reacting? If so, you should be suspicious and not continue driving.

Changing brake fluid yourself – is that possible?

This is generally not advisable – after all, it’s your safety that’s at stake. Only a specialist with the appropriate knowledge and special tools should be involved.

Can I top up the brake fluid myself?

Theoretically, yes, but we advise a trip to the workshop: Sometimes it is necessary to bleed the brake system after filling up. The specialist also knows which brake fluid is the right one.

Care should always be taken when handling brake fluid. It is harmful to health and irritates the skin and eyes. Spilled fluid in the engine compartment is best removed immediately, as it has a corrosive effect. And do not use bottles of brake fluid that have already been opened, as water may have accumulated.

How much brake fluid fits in a brake?

A rule of thumb says that 0.5 liters are needed per wheel. Basically, however, it depends on how quickly the fluid is clean, i.e. free of water. The mechanic repeatedly taps off parts of the newly filled fluid at each wheel to check the water content. After all, it is not only the fluid in the brake fluid reservoir that is changed but also the residues that are in the other components such as cylinders and lines. However, 2 liters or more per wheel is very rare.

0.5 liters of brake fluid is needed per wheel.

If the brake fluid is too low, does pumping with the brake pedal help?

If you have the feeling that there is little pressure on the brake pedal or that the travel of the accelerator pedal is too long until the braking effect finally occurs, this can have several causes. Possibly there is air in the brake system, this can be the case especially after a previous repair on the brake system or a change of the brake fluid. If neither of these applies, the brake fluid is probably old or the level in the brake fluid reservoir is too low. Pumping, i.e. depressing the brake pedal several times, increases the pressure in the brake system and the symptoms mentioned above disappear.

But beware: abnormalities in the brake system are always a cause for concern and a case for the immediate intervention of a specialist!

How to Change Your Brake Fluid - Video


Is a brake fluid flush really necessary?

Yes. Your braking system relies on the hydraulic fluid to amplify your foot’s pressure on the pedal. This is what allows you to stop a heavy, fast-moving vehicle with minimal effort.

What happens if u don't change brake fluid?

It will lead to moisture contamination in your brake reservoir where the brake fluid is stored. When you don’t change your brake fluid, your car’s braking capabilities suffer greatly it leading to poor braking performance.

David Muench (Carnes Mechanical)

David Muench (Carnes Mechanical)

Hey, I’m David. I’ve worked in a cars store for 6 years. I write reviews and guides, helping people to choose the most suitable technicals and best product for them. I’m happy to finally share my knowledge of the industry here, on CarnesMechanical.

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