Brake Fluid 101: What It Is And What Fluid You Should Be Using

So, what do you know about brake fluid besides the fact it’s really good at removing paint? Most people will just grab whatever cheap brake fluid they find at the local auto parts store, but that might not be the best choice for your application. We hit up our friends at LIQUI MOLY to learn more about brake fluid and how to make sure you’re using the right brake fluid.

The Basics Of Brake Fluid

Brake fluid is the magical elixir that transfers the force you apply to the brake pedal to the pads and rotors at each corner of your vehicle. Technically, brake fluid is a type of hydraulic fluid that is not only used in brakes, but also in hydraulic clutch systems. Brake fluid is designed to convert mechanical force into pressure, that’s how it amplifies the braking force of a vehicle’s braking system.

It doesn't matter how new your vehicle is, or how you plan on using it, you want to select the right brake fluid for your application.

There are all kinds of fluids coursing through the veins of your ride. LIQUI MOLY’s Steffen Niemietz explains what makes brake fluid different from those other liquids.

“Viscosity is a measure of the thickness of fluid at cool and hot temperatures. A higher viscosity means a slower flow of the fluid. A low viscosity at cold temperatures is needed for the proper functioning of modern brake systems equipped with ABS, ESP, or TC systems. Further requirements for brake fluids are corrosion protection and low water absorption, as well as material compatibility. So, one can say that it is a very specialized fluid.”

brake fluid

The right fluid can make all the difference when it’s time to stop a truck that is pulling a trailer.

Brake fluid is a glycol-based liquid, so it will absorb moisture from the air. It’s very important to keep any bottles of brake fluid you have sealed up to prevent them from taking on any unnecessary moisture. It’s also a good idea to keep your master cylinder closed unless you need to add fluid, this will keep moisture out of the fluid that’s already in the system. Brake fluid will go through a degradation process thanks to absorbing ambient moisture and the heat it’s exposed to during use. That’s why it’s important to replace your brake fluid on a regular basis.

The Different Types Of Brake Fluid

There are five types of brake fluid: DOT 3, DOT 4, SL DOT 4, DOT 5, and DOT 5.1. The Department of Transpiration (DOT) is one of the agencies that regulate these fluids to ensure they all adhere to the same standard and are safe. These fluids all have different applications and you need to make sure you’re using the right fluid.

Each of these classifications defines different viscosities and boiling points, which is important when you consider how much heat the fluid is exposed to during the braking process. The dry boiling point is measured when the brake fluid is new/fresh. The wet boiling point is measured with 3.7 percent water by volume, which then means it needs to be changed. It’s critical to select the right brake fluid based on how you use your vehicle, otherwise, you could find yourself with no brakes at the wrong time.

brake fluid

If your vehicle is pretty much stock and doesn’t see a lot of hard driving, DOT 3 brake fluid might be your best bet.

DOT 3 is a frequently used brake fluid in the automotive world. It’s particularly recommended for many American vehicles and can work in numerous brake systems. New DOT 3 brake fluid has a dry boiling point of 401 degrees Fahrenheit and a wet boiling of 284 degrees Fahrenheit. That’s why it’s important to replace your brake fluid on a regular basis, the reduced wet boiling point increases the likelihood of the fluid getting too hot and not working properly.

If you’re driving a European car, chances are it’s using DOT 4 or SL DOT 4 brake fluid. There are several variations of DOT 4 brake fluid and they all feature a higher boiling point as well as a lower viscosity than DOT 3. Standard DOT 4 brake fluid has a boiling point of 446 degrees Fahrenheit. SL6 DOT 4 brake fluid has a much lower viscosity than DOT 3, as well as further additives that make it particularly suitable for use in modern European vehicles. SL6 DOT 4 brake fluid has a higher overall performance compared to DOT 4 and can be used instead. You can mix DOT 3 and DOT 4 brake fluid, but it’s not recommended since there are differences between the two fluids.

Each brake fluid has its own attributes that make it the best choice for certain applications.

DOT 5 is different from DOT 3, 4, and 5.1 because it’s a silicone-based brake fluid. This fluid has a high boiling point, as the other brake fluids, 482 degrees Fahrenheit to be exact. The purple hue that DOT 5 has is different from the amber color that DOT 3 and 4 possess. Since DOT 5 isn’t a glycol-based fluid it is water-repellant and should not be used in brake systems that require a brake fluid based on DOT 3, DOT 4 or 5.1

The oddball of the brake fluid family is DOT 5.1. This fluid is glycol-based, but is clear or light amber in color. DOT 5.1 has an elevated wet boiling point similar to SL 6 DOT 4 brake fluids that can exceed 500 degrees Fahrenheit. These enhanced properties make DOT 5.1 suitable for most modern Asian and American vehicles


Selecting The Right Brake Fluid

There’s a reason you have different brake fluids to choose from. It is because different applications will have different needs. If you’re driving a stock vehicle as the manufacturer designed it to be used, chances are you’ll just need to use the brake fluid they recommend in the owner’s manual. For those who have the intention of pushing their vehicle a bit harder, a different type of brake fluid might be needed.

“Depending on the manufacturer’s specifications and the operating conditions for a vehicle, the appropriate brake fluid must be used. When you’re driving on a cold morning, you don’t want the brake fluid to be so thick that it impedes the hydraulic pressure needed to activate the brakes. The brake fluid needs to be thin so it flows easily, which means it has a low viscosity. In summary, using the right brake fluid is important for the safety, performance, durability, and compatibility of your brake system. It is important to use the brake fluid recommended by the manufacturer of your vehicle to ensure optimal performance and safety,” Niemietz states.

If you plan on really using your brakes in a high-performance setting, the brake fluid you select becomes critical. Your standard DOT 3 brake fluid isn’t going to handle lots of hard braking or a large volume of extreme braking. You’ll want to look at a racing version of DOT 4 fluid, or DOT 5.1 fluid for high-performance applications.

“The extreme requirements in motorsport and during track use dictate the use of a unique brake fluid that can withstand extremely high temperatures. Different types of brake fluids have different properties and are designed to work with specific types of brake systems. Using the right brake fluid ensures that your brake can perform at their best.”

brake fluid

If you’re going to really be pushing your ride, make sure you’ve upgraded your brake fluid and that you service your brake system often.

A brake system is a brake system, so it doesn’t matter if you have drum or disc brakes when it comes to selecting brake fluid. It all circles back to how you’re going to use the vehicle. LIQUI MOLY has an easy-to-use tool that can help you select the right brake fluid for your vehicle. Simply check the oil guide on and you will get the suitable products for your vehicle.

“Always follow the manufacturer’s instructions when selecting brake fluid for a particular vehicle.  The correct type of brake fluid is always specified on the vehicle’s original brake reservoir cap The LIQUI MOLY oil guide not only presents you with the best oils and additives, but all the suitable products for your vehicle. Of course, also the suitable brake fluid,” Niemietz says.

When in doubt, use the manufacturer-recommended brake fluid for your vehicle, or see what LIQUI MOLY suggests on its website.

According to Niemietz, people tend to make some easily avoidable mistakes when it comes to brake fluid.

“We see people try to use unsuitable brake fluids for their applications often. Another big issue is they don’t change their brake fluid on a regular basis. These can not only be costly issues when it comes to brake system issues, but they’re also dangerous.”

Not all brake fluids are created equal and have the same capabilities. It’s important to make sure the brake fluid you’re using can handle what you plan on doing with your vehicle.

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About the author

Brian Wagner

Spending his childhood at different race tracks around Ohio with his family’s 1967 Nova, Brian developed a true love for drag racing. Brian enjoys anything loud, fast, and fun.
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