Brake fluid: how long does it last and what happens if I don't change it?

Despite being one of the most affordable maintenance jobs, a brake fluid change is often overlooked. Most drivers stop carrying out this task once they no longer have to follow the manufacturer’s scheduled maintenance. And that is a mistake that can lead to serious problems.

How long does brake fluid last?

As a general rule, most manufacturers recommend replacing the brake fluid every two years, even if the car has covered very few kilometres. Some brands also set a mileage-based interval, to be applied if that limit is reached before the time limit expires. The average is usually around 60,000 km.

Recommendations can vary depending on the brand. In some cases the first change is recommended at three years and then every two years after that, so it is worth checking the vehicle’s maintenance manual

Why does brake fluid need replacing and what happens if I don’t change it?

Brake fluid tends to absorb moisture from the ambient air, and this moisture, besides lowering the boiling point and creating bubbles that reduce braking efficiency, can contribute to corrosion of the lines in the braking system through which the fluid circulates, as well as premature wear of the wheel cylinders.

You may be thinking that it is hard to see how moisture can get into brake fluid, which sits in a closed, sealed circuit. But it does: the reservoir cap is not 100% airtight and lets air in to prevent a vacuum from forming as the level drops.

In addition, this fluid is exposed to extreme temperatures. For this reason, its properties deteriorate not only with mileage but also with the passage of time.

How much does a brake fluid change cost?

A brake fluid change typically costs around 60 euros for a compact car, and can exceed 100 euros on a high-end model. Bear in mind that this figure includes the cost of the fluid itself and the labour required to drain and bleed the circuit and to remove the old fluid for recycling in line with existing environmental regulations.

How can you tell whether the brake fluid is in good condition?

As a first check, if the brake fluid loses its transparency and turns dark or you notice dirt in it, it must be replaced immediately. But be careful, because a fluid that keeps its colour is no guarantee that it still delivers its full performance.

Other signs that the brake fluid needs changing include increased brake pedal travel, or a spongy feel when you press the pedal.

There are special tools for checking the condition of brake fluid. Some are very simple and affordable, but not very reliable, since they only measure the conductivity of the fluid when the meter is inserted into the reservoir. Other, more sophisticated methods heat the fluid to measure its boiling point and check that it has not dropped.

What types of brake fluid should I use to top up the level?

It is advisable to check the brake fluid level in the car regularly, and to take it to a workshop to locate a possible leak if the level is very low or if it drops again after topping up. As is almost always the case with fluid levels, avoid going above the maximum level mark.

There are different types of brake fluid, classified according to the DOT specification, based on their dry and wet boiling points as well as their viscosity. You should use the one specified by the manufacturer.

DOT 3 fluids are now largely obsolete and are used in older cars. DOT 4 fluids are the most common today because of their better performance (higher boiling points, reaching up to 230 degrees Celsius when dry) and because they contain additives that make them absorb less water.

Be careful, because a higher number is not always more suitable. DOT 5 or DOT 5.1 fluids, for example, have lower viscosities, which can increase the risk of leaks through pores or leaks in the circuit in cars that require DOT 4 specification. It is therefore important to know what fluid your car uses and to choose one with the same specifications when topping up.

Related information of interest

• How to check fluid levels correctly: oil, coolant, brake fluid…
• Is it worth following the official maintenance schedule once the warranty has expired?
• Car engine oil: everything you need to know