BRAKEmax Blog
Water you doing? Hygroscopic brake fluid, explained.

Published on November 15, 2016 by

One of your vehicle’s most important systems is the braking system – a large part of this is the hydraulic brake fluid which should be changed out yearly.

Modern brake systems use a combination of hydraulic pressure and friction to stop your car.  Basically, when you depress your brake pedal, the brake master cylinder forces hydraulic brake fluid through the lines to your calipers or wheel cylinders, pushing pistons which initiate contact between your brake pads/shoes and the rotor/drum.

Since this system relies on friction, it will definitely get hot.  If the hydraulic fluid boils, it is useless.  Fortunately, fresh, new DOT 4 brake fluid has a boiling point of over 500 degrees so the chances of boiling are slim.  However, brake fluid is hygroscopic which means it absorbs water and moisture which enters brake fluid through microscopic pores in seals, hoses, seams, and joints at a rate of approximately 3% per year.  This water in the system now can reduce the boiling point from over 500 degrees to barely 300 degrees.  As water continues to accumulate, the boiling point drops down even further which allows for a greater possibility of fluid boiling.  Not good.

Get your brake fluid replaced yearly.  Brake fluid is inexpensive, but seals and hydraulic components are not.


This article was written by . Jeffry has worked with internet technology and graphic design for most of his life. He came to BRAKEmax in May of 2012 after a 7-year stint operating a local automotive service center. He married his wife Kerri in 2006; they have a son, Maxwell, and a daughter, Abby. When he's not at work, Jeffry enjoys cheering for the greatest sports team in the world, the Denver Broncos.

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