Everything You Need to Know about Brake Fluid

January 27, 2012

It may not cross your mind every time you stop your car, but it's brake fluid that gets the job done for you. Proper care of brake fluid is one of the most important maintenance and safety factors in the upkeep of any vehicle. Many people don't know much about brake fluid, and it can be a little bit intimidating. However, it only requires a little basic knowledge to understand the job your brake fluid does, what special precautions you should take with it and how to select the correct fluid for your car.

What Brake Fluid Does

Brake fluid is what's called a "hydraulic fluid." Most people have heard the term "hydraulic" before, but many don't know exactly what it means.  It means moved or powered by fluids. That's exactly what brake fluid does: it moves components in your vehicle's braking system. Brake fluid is special because the job it does is especially hard. It has to work perfectly under high pressures and temperatures. That's why it's so important to maintain your brake fluid under good repair, because as it ages it doesn't work as effectively.

Brake Fluid and Moisture

It's necessary to flush and replace your brake fluid periodically, because brake fluid is hygroscopic, meaning it readily absorbs moisture. That means that you should always take special care to protect your brake fluid from contact with water, especially when topping off the fluid. Brake fluid will even pull moisture in directly from the air. Over time brake fluid becomes too saturated with excess moisture, which causes it is degrade. Once moisture content reaches a certain level the brake fluid is no longer able to function properly in the brake hydraulic systems.

The DOT Ratings

One of the most common questions people have about brake fluid concerns the DOT ratings. Here are a couple common questions.

  • What do the DOT ratings mean? - The DOT stands for Department of Transportation. The DOT has placed regulations concerning the acceptable specifications for brake fluid to be used in automobiles in the US. This is to assure a uniform quality of product for everyone's safety. The biggest factor in the different DOT ratings is resistance to the effects of heat and moisture.
  • Can different DOT rated fluids be mixed? - Yes and no. Any two DOT rated fluids can be mixed without causing a harmful condition (Cross-compatibility is one of the requirements of the DOT rating). However it isn't recommended. It's important to take the utmost care in maintaining your braking system, so there's no reason to cut corners on something like mixing fluid.
  • Is a higher rating better? - Not necessarily. DOT brake fluids are backwards compatible, meaning that each new release meets or exceeds the specifications for the previous grade. What that means is that you can but DOT 5 fluid in a DOT 3 braking system, but you should never put DOT 3 fluid in a DOT 5 system.
  • What is the right DOT rating for my car? - The appropriate brake fluid for your car is decided by several factors, including the age of your car, its size, and whether it is equipped with ABS or traction control. The easiest way to be sure what type of fluid your car needs is to check your owner's manual.

Related Questions and Answers

What Tools are Required for Replacing Brake Fluid?

Replacing brake fluid is a vital thing for car owners to do in order to keep their car or truck running properly and safely. It's recommended by most car experts to replace brake fluids about every two years to prevent rust and corrosion from forming in your brake lines. If this happens, your brakes could fail. In order to replace your own brake fluid, you need to have the following tools: Eye protection, such as safety goggles; heavy work gloves to protect your hands; a box end wrench that fits your car or truck's bleeder screws; new bleeder screws if yours are shot; and some rags to wipe off things, as needed.

How Many Different Types of Brake Fluid are there?

There are several types of brake fluid. They include glycol-based fluids DOT 3, DOT 4 and DOT 5.1, as well as a silicone-based brake fluid named DOT 5. The silicone-based brake fluid is put only into vehicles with non-ABS systems. These must not have ever been filled with the glycol-based fluids. The different DOT categories refer to the different boiling points of the fluids and DOT stands for Department of Transportation. The higher the DOT number, the better quality of the brake fluid, as well as the more expensive it is. Your car's manual can tell you which one is best for your car or truck's optimal performance level.

How often should I Get Brake Fluid Service for My Vehicle?

Most mechanics recommend that car and truck owners do brake fluid service about every one to two years as regular maintenance, despite the fact that most Americans don't do this. It is a common procedure check in Europe, but there are many cars in the States that are 10 years old that have never had the brake fluid replaced. The problem with this is that after a couple of years, the brake fluid in your car will have probably absorbed a percentage of water, which makes them less reliable, and it is more susceptible to cause your brakes to fail. Since this could cause an accident, it is something you should take care of.

What Happens When there is No Brake Fluid in a Car?

It is a very bad thing if your vehicle suddenly has no brake fluid because it could cause your brakes to stop working and your car to be in an accident. Most mechanics say that brake fluid should be maintained on a schedule of replacement about every 30,000 miles. If you suspect your car is leaking brake fluid, you should have it checked by a mechanic to see what is causing the problem before the lack of fluids causes you to have major issues with your vehicle.

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