Look through the maintenance schedule in the average owner’s manual and you probably won’t find a specific change interval for brake fluid. But, just because no specific time or mileage recommendations for replacing brake fluid exist, doesn’t mean you should ignore it, especially if you are using your car for competition purposes.
As a rule of thumb, the minimum preventative maintenance interval for brake fluid should be at least every two years, more frequently, if the vehicle is used in a high performance, or heavy duty use environment. Brake fluid should always be changed when the brakes pads or shoes are replaced or when replacing a caliper, wheel cylinder, brake line, hose or master cylinder. Bleeding and flushing brake fluid is the best way to minimize the danger of fluid boil and internal corrosion in the brake system.
DOT3 and DOT4 brake fluid contains glycol, as well as various corrosion inhibitors and seal conditioners. When brake fluid is manufactured, it contains no moisture. But the properties of brake fluid make it hygroscopic in nature, meaning it attracts water.
Moisture contamination causes several things to happen. When the fluid absorbs water, it lowers the fluid’s boiling temperature. DOT3 brake fluid, which is most commonly used in domestic cars and light trucks, has a minimum dry boiling point of 401ºF. A 3% level of water contamination will lower the boiling point 25% or 100ºF!
After just one year of service, DOT3 fluid may contain as much as 2% water. After 18 months, the level of contamination can be as high as 3%. And after several years of service, it’s not unusual to find brake fluid that has soaked up as much as 7-8% water. The problem is even more acute in older vehicles due to internal seal wear and porosity in the brake hoses. Replacing your hoses with a Goodridge G-Stop Brakeline Kit with stainless steel brake lines goes a long way toward reducing this possibility.
Under normal driving conditions, neglected brake fluid may not pose a serious safety concern. The calipers on most cars and trucks won’t get hot enough in everyday driving to make the fluid boil. But under severe conditions, such as: driving down a mountain, towing a heavy trailer or the occasional track day, the brakes may get hot enough to make the fluid boil. Braking generates a lot of heat. A quick stop from 40 or 50 mph can raise the temperature of the front rotors a couple hundred degrees. Several hard, quick stops in rapid succession or riding the brakes while driving, can increase rotor temperatures to 600°F or higher. Since vapor is compressable but liquid is not, once brake fluid turns to vapor, the bubbles cause an increase in the distance the pedal must travel to apply the brakes. This is called “pedal fade” and it may result in brake failure.
You really can’t tell how contaminated brake fluid is just by looking at it. New fluid may be clear to amber-colored. The fluid will typically become darker as it ages, but this doesn’t necessarily mean it’s contaminated. If you see rust or sediment in the fluid, the fluid is long overdue for a change. High brake temperatures accelerate the rate at which the corrosion inhibitors in brake fluid break down. As the fluid ages, oxidation eats away at metal surfaces, creating dissolved acids and sludge that are carried with the fluid. These contaminants increase seal, piston and bore wear in the calipers, wheel cylinders and master cylinder. They can also damage ABS solenoid valves and cause them to jam and stick.
ATE Type 200 Amber
ATE Super Blue Racing
For performance or heavy duty applications I would recommend ATE Type 200 Amber Brake Fluid or ATE Super Blue Racing Brake Fluid. Both are designed to excel within the extreme demands made on a heavy duty or race vehicle and exceed all DOT4 standards. They are compatible with and will mix well with most DOT3, DOT4 or DOT5.1 fluids. Their formulations offer higher boiling points (wet or dry) and minimal drop in boiling point with age, resulting in a longer lasting fluid. By alternating the use of blue and amber colored fluids, evidence of a more complete system flush can be accomplished. When adding fluid to the system, use the type of brake fluid specified by the vehicle manufacturer (DOT3 or DOT4). Brake fluid specifications can be found in the vehicle's owner’s manual, maintenance guide, or on the master cylinder reservoir or filler cap.