Brake fluid change: how often and why?

According to the ANWB, the Dutch motoring organisation, brake fluid is usually changed every two years. The correct interval for your car is in the manufacturer’s service schedule. If the manufacturer specifies a different interval, you follow that.

The interval is in years, not in kilometres. According to brake manufacturer Bosch, the deterioration of brake fluid depends only indirectly on the number of kilometres driven. So if you drive little, the fluid ages at the same rate. How to read the schedule of your car is explained in our article on the service schedule of your car.

Brake fluid needs changing because it absorbs water and therefore boils sooner. According to the ANWB, DOT 3 and DOT 4 are hygroscopic: they attract moisture from the surrounding air. That happens slowly, even if you do not open the cap of the reservoir. That water lowers the boiling point.

When you brake, the brakes get hot. That heat also reaches the brake fluid. If the fluid contains too much water, it can start to boil. Vapour bubbles then form in the brake lines. Vapour can be compressed, fluid cannot. The brake pedal then sinks further and the car brakes with less force. According to the ANWB, the brakes no longer work properly when the brake fluid boils.

There is a second reason. According to Bosch, old brake fluid increases the risk of corrosion inside the brake system, and that can damage the ABS and ESP system. If your ABS light is on, read what to do when the ABS warning light is on.

DOT is an American standard for brake fluid. The number mainly says something about the boiling point. According to the ANWB: the higher the number, the higher the boiling point. The American standard gives two minimum boiling points per type: for new, dry fluid and for fluid that has absorbed moisture (the wet boiling point).

Source: Federal Motor Vehicle Safety Standard 116 (49 CFR 571.116). Under this standard, DOT 5.1 has to meet the same boiling points as DOT 5, but like DOT 3 and DOT 4 it is glycol-based.

The difference between dry and wet shows what moisture does. For DOT 4, the minimum boiling point of wet fluid is 75 °C lower than that of new fluid. According to Bosch, the industry advises changing the brake fluid before the boiling point of the fluid in the car drops below 180 °C.

DOT 5 is a different kind of fluid, based on silicone. According to the American standard, silicone-based DOT 5 is coloured purple. DOT 3, DOT 4 and DOT 5.1 are colourless to amber according to the same standard. The ANWB warns that DOT 5 may not be topped up with DOT 3, 4 or 5.1. Most passenger cars do not use DOT 5. Which type your car needs is in the owner’s manual and often on the cap of the reservoir.

You often notice aged brake fluid only when it is too late, for example during long braking on a descent. That is why the interval in the service schedule is so important. There are signs that point to a problem in the brake system:

Yes, the level, but not the quality. According to the ANWB, the brake fluid reservoir is in the engine bay. The reservoir usually has a minimum and a maximum mark.

1. Park the car on level ground and open the bonnet.
2. Find the reservoir. The owner’s manual shows where it is.
3. Check that the level is between the minimum and maximum marks. Do not open the cap unnecessarily, because that lets humid air reach the fluid.
4. If the level is below the minimum mark, have the car checked for a leak. Topping up does not fix the cause.

The level also drops a little as the brake pads wear, because the caliper pistons then sit further out. A low level can therefore also mean that the brake pads need replacing. Read more on our page about brake replacement in Rotterdam.

An electric or hybrid car also has brake fluid that ages. An electric car brakes on the electric motor much of the time and uses the wheel brakes less. The brake pads therefore wear more slowly, but the brake fluid absorbs moisture all the same, because that happens with time and not with kilometres. Here too, the interval is in the manufacturer’s service schedule. Tesla, for example, specifies for the Model 3 that the brake fluid is tested every 4 years and replaced if needed. Tesla adds that heavy brake use, such as towing, mountain descents or performance driving, can make more frequent checks and replacement necessary.

Other makes often use the familiar two-year interval. So check the schedule of your own car. What else is different about the brakes of an electric car, such as rust on discs that are used little, is explained in our article on the brakes of an electric car. Our mechanics hold the GMTO certificate, the Dutch qualification for working on high-voltage systems in hybrid and electric cars. Everything we do on brakes is on the page brake replacement in Rotterdam.

During a change, the old brake fluid is removed from the system, new fluid is added and the whole brake system is bled. Bleeding means that the old fluid and any air are let out of the lines at each wheel, until only new fluid comes out. That is done wheel by wheel, in the sequence the manufacturer specifies.

Whether the brake fluid is due at the next service is in the service schedule of your car. With a major service (in Dutch) the brake fluid change is included when the schedule calls for it. More about the full service is on the page about a car service in Rotterdam.

According to the ANWB, changing the brake fluid costs € 50 to € 75 on average. The price depends on the car, the type of brake fluid and whether diagnostic equipment is needed for the ABS and ESP system. If you have the brake fluid changed during a service, it is combined with other work.

With us you get a quote in advance and we only do the work with your approval. Call +31 10 479 00 00 with your registration number (kenteken) for a quote.

Yes. According to the ANWB, you may top up if the reservoir is no longer full, with the type the manufacturer specifies. A dropped level can, however, point to a leak or worn brake pads. So have the cause checked.

Use the type stated in the owner’s manual or on the cap of the reservoir. The ANWB warns specifically that DOT 5 may not be topped up with DOT 3, 4 or 5.1. If in doubt, ask your garage before you top up.

Yes. Brake fluid absorbs moisture even when the car is standing still. According to Bosch, the deterioration depends only indirectly on the number of kilometres. So stick to the interval in years.

Yes. An electric car has a hydraulic brake system with brake fluid, like a car with a combustion engine. There too the brake fluid absorbs moisture. Follow the manufacturer’s service schedule: Tesla, for example, specifies a test every 4 years for the Model 3, many other makes every two years. Read more in our article on servicing an electric car.

That differs per car. On a car where the ABS and ESP system also has to be filled with diagnostic equipment, it takes more time. If you combine it with a service, we tell you when you book how long the car will be with us.

No, not reliably. New brake fluid is usually clear and darkens over time, but the colour says little about the water in the fluid. Bosch calls testers that only measure conductivity very inaccurate. According to Bosch, a tester that heats the fluid and measures the actual boiling point is more reliable.

No. At the APK, the compulsory Dutch vehicle inspection, the inspector only checks that the level in the reservoir is not below the minimum mark and that the cap is fitted. The quality or age of the fluid is not measured. A pass at the APK therefore says nothing about whether the brake fluid is due.

• ANWB: Brake fluid: change or top up? (in Dutch)
• Electronic Code of Federal Regulations: 49 CFR 571.116, Standard No. 116: Motor vehicle brake fluids
• Bosch: Interview on brake fluids (in Dutch)
• Tesla: Model 3 Owner’s Manual (EU): Maintenance Service Intervals