Brake Tech: Fluid

Due to the extreme operating temperatures of a high-performance brake system, standard “parts store” brake fluids are not recommended. Of critical importance in determining a fluid’s ability to handle high-temperature applications are its 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 minimum temperature dry boiling point available in a DOT 3 fluid is 401° F, while in a DOT 4 fluid it is 446° 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° F, while DOT 4 is 311° F.

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. Glycol based DOT 3 & 4 fluids are hygroscopic; they absorb brake system moisture, and over time the boiling point is gradually reduced.

Wilwood does not recommend using DOT 5 silicone fluid in any racing applications. DOT 5 silicone fluid is not hygroscopic, so as moisture enters the system, it is not absorbed by the fluid and results in beads of moisture moving through the brake line, collecting in the calipers. It is not uncommon to have caliper temperatures exceed 200° F, and at 212° F, this collected moisture will boil causing vapor lock and system failure. Additionally, DOT 5 silicone fluid is highly compressible due to aeration
and foaming under normal braking conditions, providing a spongy brake feel. DOT 5 silicone fluid is best suited for show car applications where its anti-corrosion and paint friendly characteristics are important. Try Wilwood’s FIVE DOT 5 Silicone Brake Fluid for these applications.

Whenever you add fresh fluid to your existing system, it immediately becomes contaminated, lowering the boiling point of the new fluid. For maximum performance, start with the highest dry boiling point available. Flush the system completely and flush it regularly, especially after severe temperatures have been experienced. If necessary, to ensure degraded fluid and contamination have been completely removed from the system, disassemble, clean and rebuild brake system components.

Try Wilwood’s DOT 4 EXP 600 Plus Racing Brake Fluid or DOT 3 Hi-Temp° 570 Racing Brake Fluid.