This is because as the fluid repels any water ingress, it causes it to pool at low points within the brake system, usually the caliper, since water is heavier than brake fluid it will settle at the lowest point. The bad news is that any water that does enter the brake system, via seals or microscopic pores in the lines etc., will effectively reduce the boiling point of the whole brake system to that of water - just 100Â☌. When brake fluid reaches 8 water content the boiling point of Shell DOT 3 brake fluid has been reduced almost to that of water - 100☌ So where does this water come from Glycol based fluids are hygroscopic which means they absorb water/moisture from the environment at normal atmospheric pressures at a rate of 2-3 per year.
This means that there are no wet or dry boiling temperatures to worry about, the boiling point stays constant and never drops. Unlike DOT fluid, Mineral Oil is hydrophobic and does not absorb moisture from the environment. In some cases, Mineral oil is used in braking systems. It also prevents localized corrosion of internal parts which can be caused by water pooling in the brake system. This helps to keep the boiling point of the entire brake fluid high rather than having pools of water in the system which will boil much sooner than the rest of the brake fluid. As we've learnt, water mixed with DOT fluid has an adverse effect on the brake fluid by reducing it's boiling temperature and therefore reducing it's performance.Īs water enters the system, instead of pooling in low spots (such as the calliper), due to it's weight in comparison with brake fluid, it is dispersed throughout the whole of the brake fluid.
This water content finds it's way into the brake fluid via microscopic pores in brake hoses, seals, joints and seams. This process is exasperated in more humid conditions and climates. Glycol based fluids are hygroscopic which means they absorb water/moisture from the environment at normal atmospheric pressures at a rate of 2-3% per year. "The hygroscopic nature of DOT brake fluid is actually an advantage in a major way.
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