Brake Fluid – Buying Guide, Opinions and Analysis
Brake fluid is one of the most important safety components of any car, for this reason it is essential to perform good maintenance and know how often it must be changed or serviced, so that the car always has good braking capacity. Builders’ recommendations state that brake fluid should be changed every two years, and since it is very easy to replace, you can do it yourself at home. In this article we will analyze some of the best brake fluids on the market, such as Brembo L 04 005 , which offers you the confidence of the leading brand in brakes on the market, or Repsol RP701B96 , a high-performance product with good stability. thermal.
After our comparison of brake fluids in which we have analyzed the best products in detail, we are going to move on to the buying guide, in which we will explain which are the most important points you should pay attention to before buying brake fluid for your vehicle.
We start this guide to buy the best brake fluid with one of the most important points and that is that not all fluids on the market are the same. It is very important to use only the type of liquid indicated by the manufacturer. To find out what it is, the best you can do is consult the manual or ask directly at your trusted workshop.
Nowadays, many cars circulate with the fluid in poor condition or use a fluid that is not correct, which can cause accidents and braking problems.
In the market we can find DOT 3 type liquids, which is the most conventional liquid, they have a dry boiling point of 205 ºC and in wet conditions of 140 ºC, so they have relatively low points, which leads to the formation of foam and bubbles. Its viscosity is usually around 1500 cSt (viscosity units) and it is a common and inexpensive liquid, although practically in disuse.
DOT 4 is the most used in ABS type brakes, so it is the most common fluid today and the one that all cars usually carry when they leave the dealership. It has a dry boiling point of 230 ° C and a wet boiling point of 155 ° C, although some high-performance DOT 4s exceed these numbers. Its viscosity is 1800 cSt and offers greater durability than DOT 3, so it can be changed every 60,000 km or 3 years, although it is not recommended.
The DOT 5 type brake fluid is the most used in American cars, it is a product whose synthetic-based formulation does not use minerals, so it produces less waste and pollutes less. This liquid should never be mixed with DOT 3 and DOT 4 liquids, since they do contain mineral elements in their formulation. Due to its synthetic base it is very resistant, with boiling points above 260 ºC.
Finally, we find the DOT 5.1 type liquids. Contrary to what it may seem, it is not an evolution of 5.1, but it is a completely different liquid, with a mineral base. It has a dry boiling point of 270 ºC and a wet boiling point of 180 ºC, with a viscosity much lower than that of other liquids, 900 cSt. The main advantage of this liquid is that it has a higher hygroscopic power than DOT 3 and DOT 4, which means that it absorbs moisture better, protecting the liquid for a longer time.
Boiling point is another very important factor to look for when choosing brake fluid and it will have some impact on how much the product itself costs.
This characteristic is decisive to avoid the maximum temperature effort, since when it exceeds this point, the liquid begins to boil and steam bubbles form, making it stop being stable and causing vapor lock that prevents the car from braking correctly. When this happens, the pressure point of the pedal varies and can even get lost with a disastrous result.
Brake fluids have two boiling points: dry and wet. The first is the boiling point of the new and sealed liquid, and it is usually around 240 for a cheap liquid or 300 ºC for competition ones. The second is the boiling point of the liquid when it contains 3.5% water, something common due to condensation and possible leaks that cause water to enter the tank.
Brake fluids usually have two basic formulations to choose from: glycol-based or silicone-based. Glycol-based liquids have a better hygroscopic factor, meaning that they bind and absorb water. Those based on silicones do not have this positive property and, therefore, tend to have a lower performance.
Viscosity is the factor in charge of ensuring the functions of the braking system. The use of modern ESP brake and ride stabilization systems require high modulation speed and brake pressure.
For this reason, the best brake fluids have a particularly low viscosity, which is the prerequisite for reliable control and instant braking. Using a fluid with the wrong viscosity can have fatal consequences on brake performance.
Frequently asked questions
Q1: How to change the brake fluid?
The process of changing the vehicle’s brake fluid is somewhat more complex than changing other fluids, such as oil. The main cause is that we must not only change the liquid, but also purge the system, so that everything works correctly. We will start by parking the vehicle in a flat area. We open the hood and look for the liquid reservoir, which we will empty using a syringe or aspirator. Next, we add the new liquid, taking as little time as possible in the process to reduce the presence of air.
The next step is to bleed the brakes. To do this, we will remove the wheels, one by one and starting from the rear left. Then we will continue with the rear right, front left and front right. This order is important and must be respected. Each brake caliper includes a bleeder in the cylinder, which we must open and connect a rubber sleeve to collect the old fluid. For bleeding, you must help another person, who will step on the brake several times to “load” the system and then step on it all the way, previously opening the bleeder. It collects the excess liquid and, once the pedal is fully engaged, the drain is closed. At the end of the process, we must check the liquid level and add more if necessary. We will repeat the process with each brake until all four are completed, finally checking the level.
Q2: When to change brake fluid?
As with oils and other engine fluids, the maintenance interval appears in the manual of our vehicle, this being the main reference in this regard. If you do not have the manual at hand, in general a maintenance period of about 30,000 to 40,000 kilometers is established. Since it is an economic and vital operation for our safety, it does not hurt to execute it with an adequate frequency.
Q3: What happens if I run out of brake fluid?
Given that the vehicle’s braking system is hydraulic, what we will notice at the moment is that, when the pedal is pressed, it will go to the bottom without any effort, since that lack of fluid eliminates the resistance of the pedal itself. Obviously, the brakes will not work either, since there is no internal pressure in the system, they will not activate and you will not be able to stop the vehicle normally. In this case, you will need to use the gearbox to slow the vehicle down, using the parking brake when the speed is slow enough to stop safely.
Q4: Where do you put the brake fluid?
The brake fluid is poured into a reservoir located inside the engine compartment and properly labeled as such. Its size is small, similar to that of a small jar, so you will have to refine your view. If you cannot find it, you can always refer to the user manual, where its specific location is indicated.
Q5: What color is the brake fluid?
New brake fluid is clear and has a golden yellow hue. As it is used, it takes on a darker color to the point of turning black if it is of considerable age. This color is just one of the useful references to know if it is time to change it.