Did you know that DOT 3 and DOT 4 brake fluids are glycol based and absorb moisture over time? Moisture contamination causes the fluid boiling point to drop which could lead to fluid boil and brake fade during hard use. Moisture contamination also contributes to internal corrosion in the calipers, wheel cylinders, and steel brake lines. The reason for replacing brake fluid periodically is to get rid of contaminated fluid and restore fluid heat and corrosion resistance.
Believe it or not, moisture can actually seep in through microscopic pores in rubber seals and hoses. It also enters every time someone opens the master cylinder reservoir to check the fluid level. That’s why most fluid reservoirs are translucent, so that the level can be checked without having to open the lid. Brake fluid is hygroscopic, meaning it attracts water. Leaving the lid off a can of fresh brake fluid can ruin it overnight. It will absorb so much moisture from the air that it becomes too badly contaminated to use.
By the time a new car is only 12 months old, its brake fluid contains about 2% water. After 18 months, the water content is approaching 3%, which is enough to lower the boiling temperature of the fluid by 25%. After several years of service, it is not unusual to find brake fluid containing up to 8% water. For this reason, many experts recommend replacing the fluid as a preventive maintenance service every two years or 24,000 miles. At the very least, the brake fluid should be replaced when brakes are relined.
- Clean the top of the reservoir carefully…
- If the reservoir is not translucent, open the top of your brake fluid reservoir…
- Look to see where the fluid level lies; make sure that the brake fluid level is within half an inch or so of the cap….
- Check the color of your brake fluid. If it is not clear, it should be serviced.
Mark Martin’s Auto World checks your brake fluid FREE of charge during your routine service.