Did you know that brake fluid absorbs moisture? It’s estimated that brake fluid will pull in about 3.5% of its volume, in moisture within a year's time. The collection of moisture can lead to corrosion within your hydraulics system. It can also cause other problems such as lowering the boiling point, which results in brake fade. These changes cause your brakes to be less effective, decreasing your ability to stop in critical driving situations.
Brake fluid has hygroscopic properties - meaning that it absorbs moisture during its life in your car as it travels through your brake lines and hoses. As the water content in the brake fluid increases, the temperature the liquid boils at decreases.
What's so bad about water in the brake fluid? Well, brake fluid is incompressible under pressure, and since it has a high boiling point, the heat from your brakes isn't enough to cause it to boil. But water has a much lower boiling point. Once the moisture-contaminated brake fluid starts boiling, it creates gas bubbles. Gas is compressible. So when you step on the brake pedal and create hydraulic pressure in the brake system, instead of that force being transferred to your brake pads in order to grip your rotors (or drums) and slow your car down, that force is wasted compressing that gas.
In more practical terms, it could mean your brake pedal just sinks to the floor without stopping the car. That, friends, is very bad.
Water in your brake system can also cause rust, which can gum up the small passages in the brake lines or brake hardware, and cause your brakes to work improperly or even drag – a situation where the brake pads don't disengage from the rotor or drum, creating friction and heat, and perhaps causing even more damage.
Luckily, rather than guessing or testing to see what the moisture content is, you can just follow the manufacturer's brake fluid replacement requirements. That way you know you have clean, effective fluid that won't let you down when you need to stop. If you drive something that doesn't have a recommended interval, the rule of thumb is every two years. For high-performance cars that see spirited driving or time on the track, try to replace it every six months. For pure race cars, brake fluid is generally replaced every race. As you can see, the harder you'll be on the brakes, the more frequently you'll want to change your fluid.
Recommended service is every 1 – 2 years
Red Line now offers its own high-performance brake fluid perfect for street or track use. RL-600 is engineered to maintain viscosity, lubricity and compressibility at extreme temperatures to help safeguard against brake fade and vapour lock in racing, performance and street applications.