Most manufacturers recommend replacing brake fluid around every 30,000 miles or 24 to 36 months. The number one reason behind this is water contamination which accumulates from everyday use of the vehicle. Water contamination results in a decreased boiling point for the brake fluid, which can lead to brake failure when the brakes get hot. Longer times between brake fluid service result in higher water content in the fluid and lower boiling points. Dot 3 brake fluid is the industry standard, but Dot 4 and especially Dot 5 fluids absorbs moisture at a slower rate.