Brake fluid is hygroscopic.  Hygroscopic is the ability of a substance to attract and hold water molecules from the surrounding environment. This is achieved through either absorption or adsorption with the absorbing or adsorbing substance becoming physically changed somewhat.   A new bottle is considered “dry” with a higher boiling point.  However, since it’s a hygroscopic fluid it will absorb water over time lowering its boiling point to the “wet” level.

When it comes to boiling points for your daily driver the wet boiling point number is more important than dry because the fluid stays in your car for a long period of time.  After months or years of changing climate conditions (temperature & humidity) the brake fluid performance is closer to the wet boiling point than the dry boiling point.

Once brake fluid soaks up moisture it thickens and will not be able to withstand the heat created under the pressure of heavy braking. What happens next is a significant drop in performance and in the fluids boiling temperature. When the fluid boils it turns some of the brake fluid into vapor and forms air bubbles.  The end result is a soft or spongy brake pedal.  Another indication of this is there will be significantly more pedal travel.

G-Loc Brakes, LLC does not recommend using a silicone based brake fluid with any of its products. For more information, please scroll down to the bottom of the page to the section labeled “A word of caution.”