Silicon brake fluid (SAE J1705, DOT 5) has some cautionary characteristics. Silicon fluid compresses under pressure, which can cause a slightly spongy brake pedal feel. Silicon fluid also attracts air more than glycol fluid fluids (SAE J1703, SAE J1704 DOT 3 & DOT 4), which makes brake bleeding harder. Silicon brake fluid also tends to vaporize slightly just below its boiling point; and it will aerate from prolonged vibration. All of these factors mean that DOT 5 silicone fluid should never be used in an antilock brake system (ABS). ¹Additionally, Silicon tends to have a much lower viscosity; in other words, the fluid flows more easily relative to temperature.

Silicon brake fluids allow for air to fit in-between the individual molecules, more so than DOT 3 or DOT 4 fluids. These are microscopic air bubbles that become isolated in the brake fluid thereby dramatically increasing the amount of softness within the braking system. Because silicone fluids attract air, the end result is more compressibility. When air contaminates your fluid you now have a “mushy” or “spongy” brake pedal. Even DOT 3 and DOT 4 brake fluids have some compressibility but when air enters your system it only makes matters worse.

When compared to glycol based brake fluid, silicone brake fluid has high air solubility. More specifically in the formulation; there is 16% ± 3% dissolved air relative to the 5% ± 2% dissolved air in common glycol based brake fluids. ² Generally speaking, when brake fluid temperatures increase the dissolved air turns into a gas and ultimately creates a soft pedal and vapor lock. Bottom line, silicone brake fluids have both very high wet and dry boil points but attract air which leads to high compressibility, sold pedal and vapor lock at ambient temperatures and only increases when you are at higher altitudes.

Note: GS610™ is formulated to deliver the high boiling characteristics found in silicone-based fluids, but without the negative side effects of high air solubility. GS610™ is a superior high performance brake fluid formula designed for extreme braking conditions compared to glycol based brake fluid, silicone brake fluid has high air solubility. More specifically in the formulation; there is 16% ± 3% dissolved air relative to the 5% ± 2% dissolved air in common glycol based brake fluids. ² Generally speaking, when brake fluid temperatures increase the dissolved air turns into a gas and ultimately creates a soft pedal and vapor lock. Bottom line, silicone brake fluids have both very high wet and dry boil points but attract air which leads to high compressibility, sold pedal and vapor lock at ambient temperatures and only increases when you are at higher altitudes.

Sources:
¹AAA, web site: www.csaa.com
² Society of Automotive Engineers (SAE) J1705 revised proposed draft Jun 2004