AMSOIL Inc. brake fluids exceed government standards. The Series 500 DOT 3 High-Performance and Series 600 DOT 4 Racing brake fluids maintain a stable viscosity over a

wide temperature range and provide lubrication throughout the system. Their additive packages can raise boiling points to more than 232 degrees C (450 degrees F.) They keep water in suspension, slowing its effects on the brake system.

Brake Fluid Basics from Wilwood

Due to the extreme operating temperatures of a high-performance brake system, standard off-the-shelf brake fluids are not recommended. Of critical importance in determining a fluid’s ability to handle high-temperature applications is the Dry Boiling Point and compressibility.

The Dry Boiling Point is the temperature at which a brake fluid will boil in its virgin non-contaminated state. The highest temperature Dry Boiling Point available in a DOT 3 fluid is 572 degrees F.

The Wet Boiling Point is the temperature a brake fluid will boil after it has been fully saturated with moisture. The DOT 3 requirement for wet boiling point is a minimum temperature of 284 degrees F.

DOT 3, DOT 4, and DOT 5.1 glycol-based brake fluids are hygroscopic, meaning that they absorb moisture. There are many ways for moisture to enter your brake system. Condensation from regular use, washing the vehicle, and humidity are the most common, with little hope of prevention. However, contrary to popular belief, water that has been absorbed into glycol-based fluids will not in itself cause corrosion or oxidation the way that free-floating water and vapor could in a system that is filled with DOT 5 silicone fluid.

Silicone fluid does not absorb moisture. As a result free water vapor within the system will be more corrosive and likely to cause oxidation of any ferrous components. In addition, the water will vaporize and boil at a much lower temperature and contribute to brake fade at water’s boiling point, rather than the higher boiling of glycol-based fluids that have absorbed that moisture. Knowing in advance that most drivers will not maintain a regular fluid maintenance interval, auto manufacturers specify glycol-based fluids for that reason.

Many racers were initially attracted to silicone fluids because of the high-rated boiling points compared to most standard DOT 3 or 4 fluids. However, the chemical composition of silicone fluid causes it to be far more

compressible and easily aerated as compared to glycol-based fluids. Aeration and high compressibility can give a spongy brake pedal feel that never goes away, and can also reach a pedal fade point far sooner in competition than glycol-based fluids, therefore glycol-based fluids are always preferred for competition. Also, DOT 5 silicone fluids are not compatible with ABS systems. DOT 3, 4, and 5.1 fluids contain lubrication additives that are necessary to keep ABS internal components functioning properly.

Since silicone fluids do not absorb moisture, systems using silicone must be flushed and maintained at more frequent intervals than glycol-based fluids. The typical life expectancy of glycol-based fluids is about two years. As the moisture content of glycol-based fluids increases with time and exposure to atmosphere, the color changes from light clear or amber to a darker brown color. Local climate will impact the life cycle of fluid, based on average humidity.

The primary advantage to using silicone fluid is that it is paint friendly. Some motorcycle manufacturers also specify silicone fluid because of the effects that glycol-based fluids can have on some plastics.

Owners of show cars that use silicone fluid to prevent paint damage in the case of a spill or leak must also flush their system at periodic intervals to make sure that any moisture that may have entered the system be evacuated to prevent localized corrosion and the possibility of vaporization under heat that would cause pedal fade.

DOT 3, 4, and 5.1 glycol-based fluids are fully compatible with each other, however they will not mix with DOT 5 silicone. When mixed together, silicone fluid and glycol fluids will form a gel-like sludge in the brake system. Anyone considering changing from one fluid type to another must take all necessary measures to be sure the old fluid has been completely eliminated from the system.