Risk of accidents from water-contaminated brake fluid.
Water contamination lowers the boiling point of oil. Air bubbles form, rendering the braking system ineffective when it overheats.
Approximately half of passenger cars and trucks with more than 10 kilometers on the odometer in the U.S. have never had their brake fluid changed. Many European countries have mandated periodic brake fluid checks, and nearly half of those have been found to have faults.
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Brake fluid plays a crucial role in maintaining driving safety. Technology experts recommend that car owners replace brake fluid if it becomes contaminated with water or dirt, or replace it periodically every 1-2 years.
Experts explain that brake fluid contains glycol, a substance that strongly absorbs water. Over time, moisture can seep through the rubber hoses and seals. This phenomenon is particularly noticeable when the vehicle is used in environments with high humidity.
Brake fluid can become contaminated with up to 2% water after one year of use, and 3% after 18 months. It's not difficult to find samples with 7-8% water if the vehicle has been in use for several years.
According to an investigation by the U.S. National Highway Traffic Safety Administration, up to 20% of the 1,720 vehicles surveyed had brake fluid contaminated with more than 5% water. Water-contaminated fluid has a lower boiling point than "dry" fluid. DOT 3 fluid boils at 205°C, but when wet, it only boils at 140°C. The boiling point of most new DOT fluids is around 240 to 260°C.
With 1% water, the boiling point of DOT 3 is 187°C. With 2% contamination, it's 160°C. If there's 3% oil, it will boil at 145°C.
DOT 4 oil absorbs moisture more slowly, but its boiling point drops more significantly than DOT 3. If contaminated with 3% water, the boiling point of DOT 4 can be reduced by half.
Overheating of the brake system causes the fluid to boil, creating air bubbles. These bubbles displace the liquid in the system, rendering the brakes ineffective even when the driver applies the brakes hard. Furthermore, water contamination in the fluid accelerates corrosion of brake system components, including the ABS system.
Brake systems contaminated with water easily pass safety tests. The fluid level remains within acceptable limits, the lines are in good condition, and the brakes feel effective. However, all of this changes when the system heats up and air bubbles form.
