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Why the heck do we use brake fluids that absorb water in the first place?

Believe it or not, one of a brake fluid’s most vital characteristics is its ability to absorb water. Yes, you read that correctly – brake fluids absorb water by design and that is really a good thing.

What?

Whether we like it or not, water is everywhere and finds its way into everything. That’s just the nature of the beast. Even our brand-new sealed brake system will eventually absorb water given enough time.

The magic of diffusion allows moisture in the air to permeate microscopic pores in the rubber brake hoses, the nylon master cylinder reservoir, and the various rubber seals in the hydraulic system. Sadly, there is nothing we can do about it and if left unchecked the water would sit in our brake system and rot it away from the inside out.

Hence the need for brake fluid to absorb this unwanted house guest. Because brake fluid absorbs water into solution, the local concentration levels are typically low enough that corrosion is slowed dramatically. As an added benefit, when exposed to low temperatures, the solution state prevents the water from pooling and freezing on its own. While water in brake fluid will certainly increase the solution viscosity at low temperatures, this is much more desirable than having little chunks of ice plugging up the system!

So, the next time you are bleeding your brakes to remove the water-contaminated fluid, don’t curse at the automotive gods too loudly. After all, the fluid was only doing its job.

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