When and why you need to change the brake fluid

How often should I change the brake fluid?

So, serviceable braking system is the key to safe driving, which is why it is so important to monitor the brakes and timely change the fluid. Those drivers who do not neglect their own and others’ lives, not seldom wonder how often to change the brake fluid to comply with one of the most important frequency of replacement consumables.

Looking ahead and without making you read the whole article, I’ll answer right away – to change the brake fluid at least once after two years of operation, and if it is a sports car, then two to three times more often.

Why change the brake fluid?

Figures for the frequency of changing the “brake fluid” are not invented by the manufacturers, and are regulated relying on the fluid composition and its properties.

For reference: brake fluid’s boiling point is about 200 – 260 °С, but hygroscopicity (absorption of moisture) lowers this threshold over time, while the fluid may heat up to 150 – 180 °С in city traffic. And when this boiling point is reached, air bubbles are formed, which leads to the release of brake fluid into the reserve tank, and as a result, the low level will not create the required pressure during hard braking, the failure of the brake pedal is inevitable!

When the moisture content in the brake fluid exceeds 3% the boiling point – decreases from 30 to 50 ° C.

An equally important pretext for changing the fluid is the chemical properties of various additives, which over time, begin to decompose, contributing to the loss of their properties.

When to change the brake fluid?

Often the replacement schedule offered by the manufacturer is about 30-60 thousand km. mileage, which is about once every two years, and the presence of such an additional system such as ABS in no way affects the frequency. And if the question is about sports cars like Lamborghini or Ferrari, brake fluid replacement should be made already after 15 thousand km. as speed modes on such cars are much higher. But this data is only indicative, because if the color of the fluid has changed (a turbidity or sediment appeared), it is sometimes necessary to change the brake fluid even earlier than specified.

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Operation of the vehicle with cloudy fluid or sediment in it, can lead to malfunctions in the brake system.

Therefore, in addition to mileage figures, a good indicator of the need to change the brake fluid is its color. Although visual inspection is not the only way to monitor the condition. For example, to check the fluid, service stations use special testers, which determine the percentage of moisture and display the data on the need for replacement.

Glycol-based brake fluid is ideally recommended to be changed every 40,000 km. And if you have silicone brake fluid, there may be a completely different data on the frequency of replacement, which can be up to 5 years.

An additional reason for an unscheduled change of “brake fluid” can be depressurization of the brake system, because in addition to the fact that some of the fluid may leak, and what is left quickly enough to oxygenate and lowers the boiling threshold of the fluid.

The driver should always remember the responsibility of the question how often to change the brake fluid, because the brakes have no right to fail.

Distinctive features of DOT brake fluids.

The main differences between brake fluids are the boiling point and moisture absorption. The higher the boiling point, the better the brake fluid, but it will be more expensive.

DOT Class 3 Brake Fluid – For this class of brake fluid, the basis is a glycol (two-atom alcohol) compound. Using glycol makes it cheaper, but at the same time DOT-3 is more hygroscopic, that is, it accumulates moisture faster. And this leads to a lower boiling point in this class of brake fluid.

DOT 4 class brake fluid is a brake fluid with improved characteristics designed to work in cars with disk and ventilated disc brakes. Its basis is a compound of esters with boric acid. The boric acid in DOT-4 completely neutralizes condensed water. This produces less moisture than DOT 3 and helps to maintain a given boiling point and extend the life of the DOT 4 fluid.

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DOT-4 grade brake fluid is a high quality brake fluid.

DOT 5 class brake fluid is silicone-based and non-hygroscopic, meaning that it does not absorb moisture that enters the braking system, and this can lead to an accumulation of water in the lower points of the braking system and freezing of this water in the system at low temperatures.

DOT 5.1 Class Brake Fluid – This class of brake fluid has a composition similar to DOT-4, but, through the use of additives, has a higher boiling point. This allows the use of DOT 5.1 in high speed vehicles.

Brake Fluid Mixing: If the brake system is filled with DOT 5 (not to be confused with DOT 5.1!) do not mix DOT 3 or DOT 4 fluid. Doing so will cause the brake system to fail.

DOT 4 brake fluids may be mixed with DOT 3 and

same fluid between each other.

It is a rule of thumb that a higher fluid class can be added to a lower fluid class and not mixed with each other. For example, if your car was filled with DOT-3 brake fluid, you can mix in DOT-3, DOT-4 or DOT-5.1. It will even improve the properties of the brake fluid.

Boiling point of new brake fluid, °C DOT 3 – 205 DOT 4 – 230 DOT 5.1 – 260

Boiling point of the “old” brake fluid, °C DOT 3 – 140 DOT 4 – 155 DOT 5.1 – 180

Viscosity of new fluid at -40 °C, mm2/s DOT 3 – 1500 DOT 4 – 1800 DOT 5.1 – 900

Boiling point. Why do I have to change my brake fluid every two years?

A car’s braking system cannot function without brake fluid – it transmits the force exerted by the driver on the brake pedal to the wheel brake. Some people think that brake fluid is designed to last the life of the car. It is not! It needs to be changed periodically. The question is, how often? The standard requirement of most automakers is to completely change the brake fluid every 2 years. And here’s why.

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Even a closed brake system gets moisture from the ambient air. Brake fluid is extremely hygroscopic, it absorbs this moisture quite actively. And when too much water accumulates in the brake fluid, there is a significant decrease in the equilibrium boiling point (this term defines its properties at the end of the life cycle, when the water content in the brake fluid reaches 3.5%), which can lead to the appearance of vapor plugs in the brake fluid. How does this happen and what is the risk? Here is an example: if the driver’s foot is constantly on the brake pedal when going downhill, the temperature of the brake fluid from the heated brake pads will rise, and as soon as a critical point is reached, the water contained in the fluid will start to boil, forming vapor bubbles in the brake system. The consequence is a loss of rigidity between the brake pedal and the brake pads.

Even the minimum water content in the brake fluid leads to a lower boiling point. When using the car in the Russian climate, an excess of moisture in the brake fluid accumulates already in two years of operation. With heavy braking in the heat it can boil, and in winter it can freeze in the parking lot.

If you do your own maintenance and look after your car, don’t forget about the brake fluid. At least, periodically check its level and refill the brake tank with new if necessary.

There are special devices for measuring the boiling point in the braking system. However, the average motorist, as a rule, does not have such a device. So just make it a rule to change the brake fluid every two years.

All the difference in DOT

Basically, brake fluids differ in their boiling point temperature and viscosity. The lower the viscosity, the easier it is for the brake fluid to pass through the lines and through the various hydraulic valves, and the faster the response will be. Brake fluids are classified according to the U.S. Department of Transportation FMVSS-116 DOT standard. The higher the DOT grade, the higher the boiling point and equilibrium boiling point.

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DOT 3, DOT 4 and DOT 5.1 classes are glycol-based (NSBF) and DOT 5 is silicone-based (SBBF) (By the way, DOT 1 and DOT 2 classes are obsolete and are not manufactured anymore). Do not mix brake fluids of different bases (glycol and silicone), it is important to know this when topping up brake fluid! If you mix fluids with different bases, the resulting mixture can split. It is no coincidence that FMVSS 116 requires DOT 5 silicone fluids to be dyed red, while all other brake fluids are either clear or amber (more precisely, in shades of light yellow to light brown). As for the DOT 5.1 brake fluid, it is not forbidden to mix it with DOT 3 and DOT 4 products.

In addition to the expiration of the “usable life” of the brake fluid, the indications for its replacement are repairs of brake mechanisms or the purchase of a used car.

Selecting the brake fluid

DOT 3 brake fluids are considered rather obsolete and are used for older cars, they are designed for use in unloaded brake systems. DOT 4 are quite universal brake fluids with improved performance, they are suitable for almost all modern cars with disc brakes. And for cars with ABS, brake fluids of DOT 4 Class 6 are used.

DOT 5.1 brake fluids (that is a modified DOT 4 – with a higher boiling point) are used on cars with higher dynamic characteristics, where thermal loads on brakes are much higher – for example, on sports cars for cities.

Special attention should be given to DOT 5 brake fluids. Thanks to its silicone base these fluids are characterized by low hygroscopicity – they do not absorb moisture and do not mix with it. DOT 5 is used mainly in cars operated in conditions of high humidity and hard conditions – with frequent acceleration and intensive braking, accompanied by high dynamic and thermal loads on the brake system.

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Our advice to car owners: do not buy the fluid that you yourself think is “the best”. We advise not to experiment and just buy brake fluid that meets your car manufacturer’s recommendations. Each automobile manufacturer has its own coding for the classes of brake fluids used in the vehicles they produce – this information can be found in the vehicle owner’s manual or specifications. These codes need to be matched with the corresponding specifications of that particular brake fluid manufacturer – this will help you quickly and easily choose the right product for your car.

In conclusion, brake fluid (except DOT 5) is quite corrosive, especially to the paint on the pads and the car body – it has an corrosive effect on painted surfaces and even rubber (DOT 3). Nisshinbo carries out special tests to find out how the coating of our brake pads behaves when exposed to brake fluid. If the brake system is good, the brake fluid should not leak, but we still test the resistance of our products to its aggressive effects.

Safety precautions should be followed when handling brake fluids. The main thing is to avoid getting it in the eyes or on the skin – and if this happens, you should immediately rinse your face and hands under running water and, if necessary, consult a doctor. If it comes into contact with paintwork, clothing or shoes, rinse immediately with plenty of water. As a toxic substance, brake fluid must be disposed of as special waste. It must not be discharged into drains. It is worth noting that brake fluid is flammable, and it is best to refrain from smoking when handling it.

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