Brake fluids for cars - types, compatibility. Brake fluid: types, features, selection issues Brake fluid density dot 3
Brake fluid is a special substance that fills the brake system of a car and plays a vital role in its operation. It transmits the force from pressing the brake pedal through a hydraulic drive to the brake mechanisms, due to which the vehicle is braked and stopped. Maintaining the required quantity and appropriate quality of brake fluid in the system is the key to safe movement.
Purpose and requirements for brake fluids
The main purpose of brake fluid is to transmit force from the master cylinder to the brake mechanisms on the wheels.
Brake fluid
The stability of a car's braking is also directly related to the quality of the brake fluid. It must meet all the basic requirements for them. Additionally, you should pay attention to the manufacturer of the liquid.
Basic requirements for brake fluids:
- High boiling point. The higher it is, the less likely it is for air bubbles to form in the liquid and, as a result, a decrease in the transmitted force.
- Low freezing point.
- The liquid must maintain stability of its properties throughout its entire service life.
- Low hygroscopicity (for glycol bases). The presence of moisture in the fluid can lead to corrosion of brake system components. Therefore, the liquid must have the property of minimal hygroscopicity. In other words, it should absorb moisture as little as possible. To do this, corrosion inhibitors are added to it, protecting the system elements from the latter. This applies to glycol-based fluids.
- Lubricating properties: to reduce wear of brake system parts.
- No harmful effects on rubber parts (O-rings, cuffs, etc.).
Brake fluid composition
Brake fluid consists of a base and various impurities (additives). The base makes up up to 98% of the composition of the liquid and is represented by polyglycol or silicone. In most cases, polyglycol is used.
Ethers act as additives that prevent the oxidation of the liquid by atmospheric oxygen and during strong heating. Additives also protect parts from corrosion and have lubricating properties. The combination of brake fluid components determines its properties.
You can mix liquids only if they consist of the same base. Otherwise, the basic performance characteristics of the substance will deteriorate, which may lead to damage to the brake system components.
Brake fluids are divided into several types. The classification is based on the boiling point of the liquid and its kinematic viscosity according to DOT (Department of Transportation) standards. These standards are adopted by the US Department of Transportation.
Kinematic viscosity is responsible for the ability of the fluid to circulate in the brake system line at extreme operating temperatures (from -40 to +100 degrees Celsius).
The boiling point is responsible for preventing the formation of a vapor lock that forms at high temperatures. The latter can lead to the brake pedal not working at the right time. The temperature indicator usually takes into account the boiling point of the “dry” (without water impurities) and “moistened” liquid. The proportion of water in the “wetted” liquid is up to 4%.
Classification of brake fluids There are four classes of brake fluids: DOT 3, DOT 4, DOT 5, DOT 5.1.
- DOT 3 can withstand temperatures of 205 degrees for “dry” liquid and 140 degrees for “wet” liquid. These fluids are used under normal operating conditions in vehicles with drum or disc brakes.
- DOT 4 is used on vehicles with disc brakes in city traffic (acceleration-deceleration mode). The boiling point here will be 230 degrees for a “dry” liquid and 155 degrees for a “wet” one. This fluid is most common on modern cars.
- DOT 5 is silicone based and is not compatible with other types of fluids. The boiling point for such a liquid will be 260 and 180 degrees, respectively. This liquid does not corrode paint and does not absorb water. As a rule, it is not used on production cars. It is usually used on special vehicles operating in conditions of extreme temperatures for the braking system.
- DOT 5.1 is used on sports cars and has the same boiling point as DOT 5.
The kinematic viscosity of all types of liquids at a temperature of +100 degrees is no more than 1.5 sq. mm/s., and at -40 it varies. For the first type, this value will be 1500 mm^2/s, for the second - 1800 mm^2/s, for the latter - 900 mm^2/s.
As for the advantages and disadvantages of each type of liquid, the following can be distinguished:
- the lower the class, the lower the cost;
- the lower the class, the higher the hygroscopicity;
- impact on rubber parts: DOT 3 corrodes rubber elements, and DOT 1 fluids are already fully compatible with them.
When choosing brake fluid, the car owner must follow the manufacturer's instructions.
Features of operation and replacement of brake fluid
Brake Fluid Operation How often do you change brake fluid? The service life of the fluid is set by the car manufacturer. Brake fluid must be replaced on time. You should not wait until her condition approaches critical.
The state of a substance can be visually determined by its appearance. The brake fluid should be homogeneous, transparent and without sediment. In addition, car services evaluate the boiling point of a liquid using special indicators.
The required period for inspecting the condition of the liquid is once a year. Polyglycol fluid needs to be changed every two to three years, and silicone fluid every ten to fifteen years. The latter is distinguished by its durability and chemical composition, resistant to external factors.
Modern designers are gradually reducing the size of the brake mechanisms, and fast cars brake quite brilliantly... After two to three years of operation, the boiling point of the brake fluid decreases to approximately 150–170 °C. What will happen if the “brake fluid” decides to boil is clear to everyone: the inevitable appearance of air jams and, as a result, failure of the braking system. There is another horror story: brake fluids are hygroscopic and, having accumulated excess moisture over time, sharply increase their low-temperature viscosity in winter. In general, there is no time for humor.
The purpose of our test is to determine the boiling point of “dry” and “wet” liquids to confirm compliance with the DOT class (US Department of Transportation requirements) or the ISO international class indicated on the consumer label. In addition, we checked the kinematic viscosity at -40 °C: we need to understand whether these liquids can be used in winter.
In November 2014, the price of purchased brake fluids ranged from 40 to 120 rubles per liter. The tests were carried out in the laboratory of the 25th State Research Institute of Chemmotology of the Russian Ministry of Defense. The results are summarized in a table and also presented in the comments under the illustrations.
Most of the tested drugs were produced in Dzerzhinsk and Obninsk. But this does not mean “one barrel”: the same Dzerzhinsk, back in Soviet times, was a kind of birthplace of auto chemicals, and therefore it is not surprising that today the old traditions are supported by various companies. As for Obninsk, many manufacturers place orders there for the production of their drugs - an example is LUKOIL. We also note that some auto chemical manufacturers do not advertise the exact production address, giving the legal address instead.
The brake fluids that failed were UNIX DOT 4, PROMPEK DOT‑4, CHIMLUX DOT-4 and RSQ PROFESSIONAL EURO DOT‑4. Their main drawback is obvious: with such crazy low-temperature viscosity, the pedal cannot be pressed in severe frost.
FELIX DOT4 liquid may boil earlier than expected. RSQ PROFESSIONAL EURO DOT‑4 suffers from the same problem. Dew 4 only fits within DOT 3 standards. Therefore, only half of the tested “brakes” can be recommended for use.
Now about the best. Both drugs from those declared under class 6 have confirmed their level - these are SINTEC EURO DOT 4 (class 6) and ROSDOT 6 (DOT 4, class 6). Among liquids with a declared DOT 4, SINTEC SUPER DOT 4, LUKOIL DOT 4 and Hi-Gear DOT4 were slightly better than others. Note that both class 6 drugs can be safely used as a replacement for DOT 4 liquids. Therefore, it is logical to recognize them as the best in our sample.
Standards, parameters, requirements
The final table shows six standards. The first three standards are for brake fluids of classes DOT 3, DOT 4 and DOT 5.1 according to the classification of the US Department of Transportation. The fourth standard is for class 6 liquids according to the international standard ISO 4925. This classification is not included in the American standard FMVSS No. 116 and is between classes DOT 4 and DOT 5.1. In Russia they like to designate it as DOT 4+ or DOT 6. The fifth and sixth standards are the requirements of the technical specifications for ROSDOT brake fluids. In fact, they are only needed to check ROSDOT liquids for compliance with their specifications.
Boiling temperature characterizes the duration of safe operation of the brake fluid. Due to its physical and chemical characteristics, it absorbs moisture from the outside, which reduces the boiling point. When this decrease reaches a critical level, further use of the fluid may become dangerous. Therefore, the discrepancy between the boiling point of a “dry” liquid is not as dangerous for traffic safety as the boiling point of a “wet” liquid (although these two indicators are most often related to each other). After all, over a couple of years of operation, brake fluid picks up an average of 2–4% water.
The indicator “kinematic viscosity at -40 ºС” is important primarily for countries with cold winters. The fact is that the vehicle’s hydraulic system is designed for a certain fluid viscosity. Up to a certain threshold viscosity value, the driver can push the brake pedal without effort or with force, thereby forcing the braking system to perform its functions, but at higher viscosity values it will be impossible to do this.
110–1
Are modern brake fluids interchangeable?
The liquid manufacturer usually indicates on the label what other liquids its product can be mixed with. But the trouble is that the consumer, as a rule, has no idea what is in his tank. No one has tested mixed liquids, so we cannot recommend such an operation. And you certainly shouldn’t add liquids with low boiling points to a modern car. In general, a complete fluid change is always preferable and safer.
111–1
Which brake fluid to buy - DOT 4 or DOT 5.1?
Buy the type of fluid recommended by the car manufacturer (for example, DOT 4). And when choosing a specific brand, you can be guided by the results of our research. For reference: in America and Japan they mainly use DOT 3, and in Europe and here they use DOT 4.
Can brake fluid change color during use?
Yes. This is a consequence of strong heating and oxidation, as well as the result of interaction with rubber parts of the brake system. In addition, the color is affected by corrosion and wear products.
The basis of the car's braking system is a hydraulic drive. Its filler (in this case, brake fluid) ensures the transfer of energy from the main cylinder of the system to the wheel mechanisms.
Trouble-free operation of the brake system depends on the following characteristics of the hydraulic fluid:
- Boiling temperature. During movement, the wheel mechanisms gradually heat up due to friction, which leads to an increase in temperature inside the entire braking system. Boiling provokes gas formation in the working fluid. The gas bubbles released during this process can form an air lock that will block the brakes. Brake fluid is hygroscopic (absorbs water vapor), therefore, as the hydraulic drive filler wears out, the concentration of water in it increases, which is why the boiling point gradually decreases.
Attention! More than 90% of brake fluid consists of auxiliary fillers and various additives. Butyl alcohol, glycol or silicone can be used as a base (less than 10% of the volume). Alcohol liquids have poorer performance characteristics and are therefore out of use. Silicone fillers are considered the best, but are expensive. Glycol-based products are most widespread. However, it is glycol and its derivatives that absorb water. Manufacturers strongly advise completely changing such brake fluids every 1-2 years.
Features of the DOT 4 standard
Road safety and vehicle operation are regulated at the state level. For this purpose, certain quality and reliability standards are being introduced. Some of these regulations are spreading outside the country in which they were adopted. These include the standards of the US Department of Transportation - DOT.
There are several editions of DOT standards. DOT 4 takes into account the operating conditions of the bulk of passenger cars and is most widespread. It means:
- glycol base brake fluid;
- boiling point of fresh liquid from 230 °C, filler that has been in long-term use - not lower than 155 °C;
- the viscosity of the liquid that was in operation at a temperature of +100 °C is not higher than 1.5 sq. mm/s, at a temperature of -40 °C - not less than 1800 sq. mm/s.
DOT 4 brake fluid is produced by a large number of manufacturers. Compliance with this standard is indicated by special markings on the packaging.
Attention! Despite the fact that DOT 4 standards have become almost a universal standard, it is difficult to produce brake fluid that meets all such requirements. This requires large-scale research work, expensive equipment and high production standards, which directly results in the high cost of the finished product. In reality, the “DOT 4” marking on the packaging is by no means an indicator of the liquid’s compliance with all the requirements of the standard.
Which brake fluid to choose
The meaning of any standardization is full compliance of the finished product with certain requirements. However, in reality, finding high-quality brake fluid is not easy. The buyer has to rely not on the provisions of regulatory documents, but on reviews of other consumers, the results of independent examinations and some indirect signs. The generalized experience of many car owners indicates the great importance of the following criteria:
- manufacturer. Domestic companies produce brake fluids of fairly high quality. The affordable price also speaks in favor of their products. However, finding a good product among all the offers is difficult. In some cases, a product that performed well at the start of sales subsequently loses quality. In others, there is a high risk of encountering a fake. The products of the largest foreign companies (in particular, Castrol, Hi-Gear, Pentosin, Mobil, TCL, Total, Tutela) are more expensive, but demonstrate consistently high quality;
- color. High-quality brake fluid DOT 4 is transparent with a yellowish or reddish tint. Cloudy color and sediment are unacceptable. Many brake fluids are sold in opaque containers. If external defects are discovered after purchase, you should not risk road safety and use such hydraulic fluid;
- consistency. Full compliance of this criterion with the requirements of the standard can only be established in laboratory conditions. When pouring, the liquid should not have the consistency of water or motor oil. When operating a vehicle in any weather conditions, the brake pedal travel should be smooth, without sudden dips, jerks, excessive resistance or complete blocking;
- price. High-quality brake fluid can be relatively cheap. However, you should avoid products that are priced dramatically differently from competing offerings.
The quality of the hydraulic fluid determines the reliable operation of the entire brake system. Liquid standard DOT 4 is suitable for most brands of cars. To purchase a reliable product that best meets the requirements of this standard, you should pay attention to the manufacturer, price and consistency.
How to choose the right brake fluid - video
Safe driving of a vehicle is impossible if its braking system is intermittent. This unit requires increased attention, since it is directly responsible for the safety of both passengers and the driver himself. In this regard, it is important to promptly replace brake fluid, which must be of proper quality and expiration date.
Today, car markets and specialized stores offer a wide selection of different brands of brake fluids. The most popular of them are Castrol and Mobil, but among the budget options there are decent compounds with excellent characteristics, for example: rosDOT or SuperDOT.
All “DOT” liquids are divided into several types: DOT 3, DOT 4 and DOT 5. Each of these compositions has its own characteristics and can only be used with certain types of machines. But, before we look at the composition of brake fluid DOT 4 and 3, it is worth saying a few words about the general characteristics of all fluids for the brake system of a car.
Differences in brake fluid composition
Compositions for the brake system differ in their base. You can still find mineral liquids based on castor oil in butyl or isopropyl alcohol. The disadvantage of such “brakes” is their low boiling point, which does not exceed 200 degrees. If the system overheats, the liquid becomes too viscous and as a result may lose fluidity altogether.
Glycol analogues are the most popular. They are made on the basis of glycols and polyglycols, as well as their esters. Such “brake fluids” are characterized by a high boiling point and excellent viscosity. The only drawback is its high hygroscopicity, which means that glycol formulations strongly absorb moisture.
There are also silicone brake fluids, which are considered one of the highest quality and “long-lasting”, but, unfortunately, they are practically not used for ordinary cars. Therefore, the best brake fluid is glycol. This type includes “dotov” compositions, the differences, classification and properties of which we will consider in more detail.
Classification of bunkers
What elements are included in brake fluids, their properties, markings - all these parameters need to be paid attention to when purchasing this or that composition. Therefore, it is worth learning more about the classification of “dotov” compositions.
Initially, the abbreviation DOT looked like USDOT and stood for United States Department of Transportation, which translates as the US Department of Transportation. As you may have guessed, this institution is responsible for the safety of vehicles. The same Department created a specification for the requirements and properties of brake fluids, and also divided several FMVSS No. 116 standards and assigned them the name DOT. This means that DOT is not the name of the liquid, but an international standard, according to which any company can be the manufacturer of this product.
Interesting! International standards such as SAE J 1703 and ISO 4925 appeared much later.
Based on this, the following compositions emerged:
DOT 3
This brake fluid is based on the simplest glycol compounds (polyethylene glycol and polyethers), and therefore its cost is an order of magnitude lower. This, of course, makes DOT 3 very popular among car enthusiasts. Like all liquids made on the basis of glycols, compositions of this class absorb moisture very quickly, and therefore their boiling point decreases over time. Because of this, DOT 3 does not have a long service life, and such a “brake guard” will have to be changed every 2 years.
Healthy! DOT 3 fluids are not compatible with natural rubber, which is what brake pads are often made from. In addition, the compositions are aggressive to paint and varnish coatings.
It is also worth noting that the viscosity of such liquids is not so much - 1500 mm 2 / s at -40 degrees. DOT 3 compounds are used for brake systems of vehicles equipped with drum brakes. The fluid is also suitable for disc brakes located on the front wheels.
DOT 4
DOT 4 fluids have better performance. In addition to glycols, they contain boric acid, due to which excess moisture in the composition is neutralized. This means that the boiling point of DOT 4 is stable and does not decrease during vehicle operation. However, the viscosity of this composition is the highest among other “pillboxes”. Therefore, it is impossible to say she is the best. In addition, the shelf life of DOT 4 brake fluid also does not exceed 2 years. In addition, the composition of this class also acts aggressively towards paint.
Healthy! On the shelves of domestic stores you can find compounds labeled DOT 4.5 or DOT 4+. There are no such classifications in the American system, so be careful.
However, Dot 4 brake fluid, whose technical characteristics are not ideal, is in great demand among owners of cars equipped with disc brakes.
DOT 5
If we talk about which brake fluid is better, then the “Dotov” composition DOT 5 is considered the most durable. The fact is that it is made on the basis of silicone, which is characterized by its weak hygroscopicity. Thanks to this, the service life of DOT 5 is 4-5 years. The remaining characteristics of the liquid are also close to ideal. Among the advantages it is worth mentioning stable viscosity, high boiling point and much more. In addition, the composition repels moisture and behaves neutrally in relation to rubber elements or paint coatings.
But in every barrel there is a fly in the ointment. The ability to repel excess water will have to be attributed to the disadvantages of DOT 5, since excess moisture does not mix with the liquid, but gradually accumulates in the lower sections of the brake system. As a result, the resulting water "apendix" freezes in winter and interferes with the operation of the system. Another problem with DOT 5 is the high degree of aeration, that is, air saturation. That is why such fluids are strictly prohibited for use in cars with ABS. Well, for those who, as luck would have it, are the owners of just such machines, a special composition was developed.
DOT 5.1/ABS
Liquids of this class are made on the basis of glycols, but, in addition, they contain a large number of additional additives. Thanks to this, DOT 5.1 has a high boiling point, low viscosity and neutrality towards rubber gaskets. However, such compositions still corrode the paint.
Such brake fluids circulate freely throughout the system, improving the performance of the brakes themselves. Due to these properties, DOT 5.1 compounds are used for racing cars, sports cars and motorcycles. The service life of such a liquid is 3-4 years.
With the advent of all these classifications, a completely logical question arises - what will happen if you mix different classes of liquids?
Can DOT fluids be mixed?
It’s worth saying right away that brake fluid, the composition of which is designed for ABS, should under no circumstances be mixed with other “pillboxes”. Active additives in DOT 5.1 are not intended for use with other types of liquids. Therefore, even DOT 5 cannot be mixed with DOT 5.1/ABS. Elements of different chemical compositions and other components, when mixed, will create an unpredictable cocktail that will not lead to anything good.
Mixing glycol fluids with silicone fluids is also not recommended. Under the influence of chemical reactions, you will receive a composition that will not meet existing requirements.
The only two compounds that behave “friendly” are DOT 3 and DOT 4, they can be mixed. However, there is one important feature here too. A higher class liquid must be added to a composition of a lower class. Accordingly, it is recommended to add DOT 4 to DOT 3. Thanks to this, you will improve the characteristics of the initial liquid poured into the system. However, if you break this rule, nothing bad will happen.
In custody
Since brake fluid generally has the properties of absorbing moisture, when purchasing a composition it is imperative to pay attention to the packaging. It must be intact, without creases or damage. It is best to purchase liquids that are sold in bottles with additional protection against tampering, or these can be bottles with necks sealed with foil.
The effectiveness of the braking system depends not only on the condition of the actuators, but also on the brake fluid. After reading this article, you will learn why it is important to use the correct brake fluid for your vehicle, what happens if you use the wrong fluid, and how to choose it.
What does brake fluid do?
The brake system of any car consists of master and working brake cylinders, which operate on the principle of communicating vessels. Pressing the brake pedal activates the brake master cylinder or the electromechanical ABS actuator, which performs the same functions. The pressure in the brake system increases because the fluid, like water, is not compressed. The rising pressure squeezes out, which presses the pads against the brake disc or drum. Intensively heats the pads to a temperature of 150-300 degrees. Because of this, the working cylinders and brake fluid heat up to 120-220 degrees. If the boiling point of the liquid is lower, the released vapor will sharply increase the pressure in the braking system, which will negatively affect the handling and safety of the car.
If the pour point of the liquid is higher than the air temperature, then braking efficiency is sharply reduced. Thickened fluid has difficulty transmitting pressure through the thin pipes of the brake system.
If the liquid is hygroscopic (has the ability to absorb water), then over time moisture from the air will penetrate into it. This will change the basic characteristics. The boiling point will decrease and the pour point will increase. Effective operation of the master and wheel brake cylinders is only possible if the brake fluid lubricates the rubber sealing parts, reducing friction against the metal surface of the cylinder. Cars produced in the 60-80s of the last century used rubber seals that corrode some types of brake fluid. This is due to increased demands on the braking system, which required the development of new fluids with improved boiling/freezing points and hygroscopicity. For such brake systems, hoses and seals made of especially resistant rubber are used.
Types of brake fluid
The industry produces three types of brake fluid:
- butyl (DOT 3);
- glycolic and polyglycolic (DOT 4);
- silicone (DOT 5).
Butyl brake fluid has a low boiling point and a high pour point, but it perfectly lubricates rubbing rubber parts without damaging them. This fluid is used only if it is recommended for the car. Glycol and polyglycol liquids boil at a temperature of 240-260 degrees, and begin to solidify only at a temperature of minus 40 degrees. In addition, they have good lubricating properties and are less aggressive towards rubber products (RTI): brake hoses and sealing rings. Silicone fluids have a high boiling point and a complete lack of hygroscopicity, but have a weak lubricating effect and destroy hoses and O-rings made of ordinary rubber. The numbers after the letters DOT indicate the approval class according to American safety standards (Department of Transport).
How to choose brake fluid between DOT 3 and 4
When choosing brake fluid, refer to your vehicle's owner's manual. If DOT 3 fluids are recommended for a car, then using others will lead to rapid failure of rubber goods. If DOT 4 fluid is recommended, then using DOT 3 will lead to a slight decrease in braking performance in cold and hot weather, and using DOT 5 will quickly destroy hoses and seals. If DOT 5 fluid is recommended, then using any other will lead to a serious decrease in braking efficiency.
The most reliable liquid manufacturers
The most reliable foreign manufacturers are the following: Castrol, Liqui Moly, Mobil. Among Russian companies, the most reliable are Tosol-sintez, Khimprom, and SV-KHIM. All of them produce their products in accordance with the requirements of DOT 3 and 4. Among Russian manufacturers, there is not a single one who produces high-quality brake fluid of the DOT 5 class, comparable to foreign products.
How to spot a fake
There are two basic rules that allow you to identify a fake;
- appearance of the packaging;
- certificate of conformity.
All serious Russian and foreign manufacturers of brake fluid pay great attention to packaging. Therefore, all containers are made without the slightest flaw, the stickers are made using a typographic method, all inscriptions and drawings (even small letters) look very clear. If the labels are applied unevenly, are not clearly printed, or if manufacturing defects are visible on the container, it is a fake. After unscrewing the lid, inspect the protective film. It must bear either the name or logo of the manufacturer. If this is not the case, this is a fake.
Brake fluid is subject to mandatory certification. It is checked by enterprises and laboratories that have received accreditation from the Federal Agency for Technical Regulation and Metrology. The certificate must indicate:
- manufacturer's name;
- name of brake fluid;
- date of inspection; certificate validity period;
- name of the organization that conducted the inspection;
- date of accreditation and registration number;
- regulatory documents according to which the audit was carried out.
If there is no certificate of conformity, or it does not contain the necessary data, this is a fake.
