Changing the brake fluid every two years for preventive maintenance can help prolong the life of the hydraulic components in the brake system. But more importantly, it can minimize the risk of pedal fade when the brakes are overworked.
The reason why brake fluid should be changed periodically is because it becomes contaminated with moisture that enters the system through microscopic pores in rubber brake hoses and piston seals. Moisture lowers the boiling temperature of the fluid, which increases the risk of fluid boil and loss of pedal if the brakes get too hot. Moisture also promotes corrosion and causes rusting and pitting in the calipers, wheel cylinders, master cylinder, steel brake lines and ABS solenoid valves.
Tests have shown that after only a year of service, the brake fluid in the average vehicle can contain as much as two percent water. After 18 months, the level of contamination can reach three percent and continue to climb to as much as eight percent or more as time goes on. As the amount of moisture in the fluid goes up, the boiling temperature comes down.
Brand new DOT 3 brake fluid must have a dry (no moisture) boiling point of at least 401 degrees F, and a wet (moisture-saturated) boiling point of no less than 284 degrees. Many new DOT 3 fluids exceed these requirements. Even so, only one percent moisture can lower the boiling point of some DOT 3 fluids to 369 degrees. Two percent water can push the boiling point down to around 320 degrees, and three percent can take it all the way down to 293 degrees — which is getting dangerously close to the minimum DOT requirements.
DOT 4 fluid has a higher minimum boiling temperature requirement (446 degrees dry and 311 degrees wet) and soaks up moisture at a slower rate.
But it suffers an even sharper drop in boiling temperature as moisture accumulates. Three percent water will lower its boiling point as much as 50 percent.
If motorists would only follow this simple advice and change their brake fluid periodically, they could greatly prolong the life of the hydraulic components in their brake system (which should save them money on expensive brake repairs over the long run). Yet half of all cars and light trucks that are 10 or more years old have never had their brake fluid changed! The average car today is almost 11 years old, so there are a lot of vehicles out there with badly contaminated fluid.
One reason why many motorists don't ask for a brake fluid change is because no one has told them about the benefits of changing the fluid. Most are also blissfully ignorant of the dangers posed by contaminated brake fluid. But the risks are real. Prolonged heavy braking, mountain driving or towing a trailer may overtax the brake system's ability to manage heat, increasing the danger of fluid boil.
A case in point: A child was killed in an accident when his parent's five-year-old minivan with 79,000 miles on it suffered loss of pedal and crashed while the family was driving in the mountains of Washington state. Fluid boil was blamed as the cause of the accident.
CHECK FLUID PERIODICALLY
For safety's sake, the condition of the fluid should be checked periodically. An electronic brake fluid tester can reveal the boiling temperature or moisture content of the fluid. You can also use newly introduced chemical test strips that change color to indicate moisture contamination (a second color patch identifies the type of fluid in the system).
In spite of the benefits that can be realized by fluid changes, General Motors and Chrysler do not mention brake fluid in their scheduled maintenance recommendations. A GM spokesman said Delco Supreme 11 DOT 3 brake fluid contains additives that many other brake fluids do not, so it is essentially a lifetime fluid. Starting in 1993, GM began using a new type of rubber brake hose with an EPM lining and outer jacketing that reduces moisture penetration by 50 percent. So GM does not consider fluid contamination to be a significant problem on its newer models.
Ford, however, recently changed its position and now recommends changing the brake fluid every 36,000 miles or three years — and to replace the fluid each time the brake pads are serviced. Several import vehicle manufacturers also recommend fluid changes for preventive maintenance. BMW says the fluid should be changed every two years, Honda recommends new fluid every 25,000 to 30,000 miles, and Subaru says to change the fluid every 30,000 miles.
ALL BRAKE FLUID IS NOT EQUAL
As any brake fluid supplier will tell you, brake fluid is NOT a generic product. Just because a fluid meets the minimum DOT 3 or DOT 4 specifications does not mean it can tolerate moisture or provide the same degree of corrosion protection as another brand of fluid. Some premium quality DOT 3 fluids now have dry boiling points as high as 550 degrees F, which far surpass the minimum DOT requirements and meets the highest OEM requirements.
So the next time you're inspecting or servicing brakes, be sure to check the condition of the fluid as well as the level. If you add or change fluid, use type specified by the vehicle manufacturer (DOT 3 or 4) and use the highest quality fluid you can get.