Today we’re looking at the subject of fluid flushes to answer the question “Do You Need a Brake Fluid Flush?”
What does Brake Fluid Do?
First, let’s talk about what brake fluid is, and what it does. As you may already know, your car’s brake system works using hydraulic pressure. The force you apply to the brake pedal is multiplied by the brake booster and used to move a hydraulic piston in the master cylinder. Then,that piston applies pressure to the brake fluid. Your brake calipers use that pressure to squeeze the brake rotor between the brake pads and stop the car. The clamping force generates friction, which turns your car’s kinetic energy (movement) into heat, and slows the car.
Since stopping generates heat, your brake system components are subjected to some pretty high temperatures. This includes your brake fluid.
What is It Made Of?
Most vehicles today use either DOT 4 or DOT 5.1 Brake Fluid. These fluids are Glycol-Ether based. In addition to a poly-glycol-ether as a base fluid, brake fluids contain various additive chemicals to give it the desired performance characteristics. Each brake fluid grade (DOT 3, 4, 5, and 5.1) must meet strict requirements as far as boiling point and viscosity. Each grade has slightly different requirements.
Since brake fluid is glycol-ether based, it is hygroscopic. This means it will absorb moisture from the atmosphere under normal humidity levels. As the moisture content rises, the boiling point of your brake fluid lowers. Moisture content will also begin to corrode your brake system from the inside out.
Do You Need a Brake Fluid Flush?
As you can see in the image above, new brake fluid is somewhere between clear and champagne colored. As it absorbs moisture, it gets cloudy and darker in color.
It has a tendency to absorb 1- to 2-percent of water in one year based on operating conditions and temperatures. One study by the National Highway Traffic Safety Administration found that 20 percent of the cars they tested had brake fluid with 5-percent moisture content. Ideally, you want to keep the moisture level below 4%, so brake fluid should be changed every 2 years or 30,000 miles. Whichever comes first. Give your favorite mechanic a call or stop by to discuss any questions you may have, or to schedule a brake fluid flush.
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