Brake Fluid

• Brake fluid is a hydraulic fluid that is used in cars, trucks and motorcycles. In vehicles with hydraulic brakes, the fluid helps transfer force into pressure. In its natural state, liquids are not easily compressed. Liquid molecules have no voids, so they pack together well, which results in bulk forces being transferred to the braking mechanism.
  
  

DOT 3 Dry Boiling Point

• The majority of brake fluids in use today are synthetic in nature. They are glycol-ether based or silicone based. DOT 3 brake fluid usually is glycol-ether based. Brake fluids are classified according to their boiling points. DOT 3 brake fluid has a dry boiling point of 401 degrees. This means that before the fluid has been put into a braking system, it will boil at 401 degrees.
  
  

Wet Boiling Point

• When brake fluid sits in a brake line, it absorbs moisture. This moisture evaporates into steam when the brakes heat up, which can interfere with brake performance. As brake fluid ages, the boiling temperature is reduced. When the moisture content of brake fluid reaches three percent the wet boiling point is established. DOT 3 brake fluid has a wet boiling point of 284 degrees.
  
  

Changing Brake Fluid

• It commonly is accepted that DOT 3 brake fluid should be changed, or flushed, every one to two years. DOT 3 brake fluid absorbs moisture from the atmosphere and when it reaches a certain water content it must be replaced. Test strips are available to test the moisture level in the brake lines.