Risk of accidents from water-contaminated brake fluid
Water contaminated oil lowers its boiling point. Air bubbles form which render the brake system ineffective when they overheat.
About half of all cars and trucks over 10 years old in the United States have never had their brake fluid changed. Many European countries require regular brake fluid testing, and nearly half of them have found defects.
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Brake fluid plays an important role in maintaining safety while driving. Technology experts recommend that car owners should change the brake fluid if it is contaminated with water or dirt or change it periodically every 1-2 years.
The reason given by experts is that brake fluid contains glycol. This is a strong water-absorbing substance. Over time, water vapor can penetrate rubber hoses and gaskets. This phenomenon appears clearly if the vehicle is used in an environment with high humidity.
Brake fluid can contain up to 2% water after 1 year of use, 3% after 18 months. It is not difficult to find samples of oil containing 7 - 8% water if the car is used for several years.
According to a survey by the US National Highway Traffic Safety Administration, up to 20% of 1,720 vehicles had brake fluid containing more than 5% water. Water-contaminated fluids have a lower boiling point than “dry” fluids. DOT 3 fluids boil at 450 degrees Fahrenheit, but when wet, they boil at 200 degrees Fahrenheit. The boiling point of most new DOT fluids is around 450 to 460 degrees Fahrenheit.
Mixed with 1% water, the boiling point of DOT 3 is 187 degrees C. Mixed with 2% is 160 degrees C. If 3% oil will boil at 145 degrees C.
DOT 4 oil absorbs moisture more slowly, but its boiling point drops more than DOT 3. If 3% water is added, the boiling point of DOT 4 can be reduced by half.
Overheating of the brake system causes the fluid to boil, creating air bubbles. Displacing the liquid fluid in the system, air bubbles render the brake system ineffective even if the driver applies the brakes hard. In addition, water-contaminated fluid accelerates the corrosion of brake system components, ABS.
The brake system with mixed fluid easily passed the safety test. The fluid level was within acceptable limits, the lines were good, and the brake pedal felt effective. But all that changed when the system got hot and bubbles formed.
