How does Brake Fluid work?
Definition: The brake system uses a glycol-based hydraulic fluid. The fluid is "hygroscopic," which means it tends to absorb moisture over time (never leave a can of brake fluid open for this reason). Moisture lowers the boiling point of the fluid and causes internal corrosion in the brake system.
That's why the fluid should be replaced when brake repairs are made or
every two years for preventive maintenance. There are several different
types, based on the boiling temperature and other characteristics of the
fluid. DOT 3 or DOT 4 is used in most passenger cars and light trucks. Use
only the type of fluid specified by the vehicle manufacturer.
Using DOT 3 in an application that calls for DOT 4 might create a safety
hazard. DOT 5 brake fluid is different from DOT 3 and DOT 4 in that it is
silicone-based. DOT 5 is NOT recommended for any vehicle equipped with antilock
brakes - but it can provide long-lasting protection against corrosion for
vehicles that are stored for long periods of time or are driven in wet environments.
Why should I flush my brake fluid ?
We often recommend that you flush your brake fluid, sometimes because it is dirty, but sometimes simply because it has been 30,000 miles since your last brake flush.
New brake fluid is both clean and clear. Dirty brake fluid is obvious. That dirt and contamination will wear on all of your hydraulic brake parts, particularly your seals, causing them to fail prematurely. But more important than the dirt in your brake fluid is what you can't see: the water.
Brake fluid is hygroscopic, which means it absorbs moisture. If you leave a can of brake fluid open overnight, it will be ruined by the moisture it soaks up from the air. This is intentional. Your brakes get so hot that they can boil water. If water in your brakes evaporates, your brakes will fade or fail. The brake fluid prevents the water from evaporating.
Over time, water will seep into your brake system through the brake lines and whenever the brake fluid cap is off. Brake fluid absorbs 1%-2% water each year. Old brake fluid can be 5-10% water, which drops its boiling point by 25-50%. In addition, the water will corrode all the brake parts it touches.
Dot 3 & Dot 4 brake fluid are common in most brake applications. Dot 5 does not attract water and is occasionally used in brake systems for that reason. However, Dot 5 must never be mixed with Dot 3 or Dot 4, and it must never be used in an ABS brake system.
