Knowledge base
Brake fluid replacement — why it is often due every two years
You never see brake fluid and you don't notice it ageing. Yet it is one of the most important fluids in your car. It carries the force of your foot to the brakes. And that fluid slowly changes, even if you drive little.
Brake fluid attracts water
Most brake fluid (DOT 3, DOT 4 and DOT 5.1) is hygroscopic: it absorbs moisture from the air. That happens very slowly, through hoses, seals and the reservoir vent. After a few years the fluid contains a few per cent of water. That happens even when the car is parked.
That is by design. The water spreads through all the fluid instead of sitting as a droplet in one spot, where it would freeze or cause rust. But it comes at a price: the boiling point drops.
Why the boiling point matters
Under hard or long braking the discs and callipers get hot, and that heat also reaches the brake fluid. New DOT 4 fluid only boils above 230 °C. With a few per cent of water that can drop to around 155 °C.
If the fluid boils, vapour bubbles form in the brake lines. Vapour can be compressed, fluid can't. The pedal then goes soft or sinks further, just when you need to brake hard, for example downhill with a full car or after an emergency stop from the motorway. Over time water can also cause corrosion in the callipers and the ABS unit.
How often should it be changed?
Many manufacturers specify a brake fluid change every two years, regardless of mileage. Some makes use a different interval, for example the first change after three years. The exact interval is in your car's service schedule.
You can't really tell by the colour: clear fluid can still hold a lot of water. A brake fluid tester measures the water content or the boiling point. If you don't know when it was last done, assume it is due now. Combine it with your service, so the car only has to come in once.
How it is done and what it costs
The old fluid is pushed out of the system at each wheel until only new fluid comes out. We use the type specified for your car. On some cars with ABS and ESP diagnostic equipment is needed to bleed the system completely.
We replace brake fluid for a fixed price of € 80, including labour and VAT. You also see this price in the service calculator, where you can tick brake fluid separately with your service — for an electric car too.
Frequently asked questions
Can't I just top up the brake fluid?
Topping up doesn't remove the water from the system. The level also drops slightly as the brake pads wear. If it drops quickly there may be a leak: have the brakes checked straight away.
Is it needed if my car does low mileage?
Yes. Brake fluid absorbs moisture over time, not over kilometres. That is why the interval is set in years.
What does a brake fluid change cost at NRG?
A fixed price of € 80, including labour and VAT. You can tick it separately with your service in the service calculator.
Is brake fluid part of the full service?
No. Brake fluid has its own interval in the service schedule. In the calculator you add it separately.
Tick brake fluid separately with your service in the service calculator or read more about brakes and servicing in Tilburg.