It means that the brake fluid absorbs water. Most all brake fluids you use in you're vehicles, automotive or otherwise will absorb water from the atmosphere right through the brake systems metal and rubber parts. You should change or at the very least, inspect your brake fluids yearly. As water is absorbed into the system, the boiling point lowers and the fluid can do very nasty things to your brake lines, abs systems and master cylinder parts.
If your brake fluid is hygroscopic then it means that is will absorb water/moisture from the air and it can effect your boiling point and your brakes may fail at high speeds.
Yes it readily absorbs moisture.
No, oil is not hygroscopic. Oil does not have a tendency to absorb or attract water molecules from its surroundings like hygroscopic substances do.
DOT 5 is silicon based and will not absorb moisture.
Brake fluid must be changed every two years at most. Since it is hygroscopic--that is, it absorbs moisture/water over time. with our tropical climate, this problem is exacerbated. Fresh brake fluid helps resist brake fade and give better brake feel and modulation.
No, the fluid cannot absorb water but you can get water in your brake system and that would be bad. --Most brake fluids used today are glycol-ether based. Glycol-ether brake fluids are hygroscopic (water loving), which means they absorb moisture from the atmosphere under normal humidity levels. Racing brake fluid may be synthetic and not have this problem, but in the everyday world, brake fluid does absorb water.
It is recommended that brake fluid be added if it is low. We usually see marks on the dipstick (on vehicles that have them) or on the side of the brake fluid reservoir. The marks will usually say "full" or "low" and can be used as indicators as to if and when to add brake fluid. There is one more thing. Manufacturers and service professionals usually recommended that brake fluid be changed every two years. Brake fluid is hygroscopic, which means it absorbs water. If brake fluid absorbs atmospheric moisture over a period of time, the boiling point of the fluid will drop. Under extreme conditions, the fluid could boil causing catastrophic failure of the brakes.
It absorbs water.
Most car makers recommend that the brake fluid be changed every two years. The make/model of the vehicle is not an issue, it is just that brake fluid has a "life span" of about 2 years once it is in use. Brake fluid is "hygroscopic", which means it absorbs water from the air, so after about two years of use it needs changing.
Generally contaminated brake fluid is very dark and grimy looking. It also may cause a spongy brake petal, but not always. If you have reason to believe that your brake fluid is contaminated, you should definitely have it changed. If there is more than 3% water in your brake fluid, you run the risk of super heating the water causing one or more of your brake lines to explode, which apart from being incredibly dangerous is also tremendously expensive to repair. Brake fluid is very hygroscopic, and when exposed to air, it readily absorbs water.
Mineral brake fluid is composed of mineral oil and additives, while other types of brake fluids, such as DOT 3, DOT 4, and DOT 5, are made from glycol-based compounds. Mineral brake fluid has a higher boiling point and is less hygroscopic compared to glycol-based brake fluids, making it more suitable for high-performance vehicles.
No, but it's also completely incompatible with the stuff in your car now and it's very expensive. As to the fluids that don't require you to flush the brake system two or three times when changing over, try a good brand-name DOT 4 fluid.