NOTE: Only use fresh un-opened fluid. Once opened, use immediately. Do not store opened bottles or cans, or reuse old fluid.
Due to a high-performance brake system's extreme operating temperatures, standard parts' store brake fluid is not recommended. Never mix brake fluids of different DOT classifications.
Dry Boiling Point
Of critical importance is the brake fluid's dry boiling point - the temperature at which a brake fluid will boil in its virgin non-contaminated state. The minimum dry boiling point temperature is 401° F for DOT 3 fluid, and 446° F for DOT 4. All Wilwood brake fluids exceed these standards, with Hi-Temp° 570 rated at 570° F, EXP600 Plus rated at 626° F, and XR Race-Only at 645° F.
Wet Boiling Point
Moisture enters your brake system through condensation, weather, ambient humidity, or washing the exterior. Glycol based brake fluids are hygroscopic (they absorb moisture), and over time the boiling point is gradually reduced. The DOT 3 minimum wet (roughly 4% water absorbed) boiling point temperature is 284° F, DOT 4 is 311° F. All Wilwood brake fluids exceed these wet boiling standards, with Hi-Temp° 570 rated at 313° F, EXP600 Plus rated at 417° F, and XR Race-Only at 432° F.
DOT 5 Silicone Fluid
Silicone DOT5 fluid is often used in classics, show cars, and pre-ABS Harley-Davidson motorcycles to prevent corrosion. Silicone fluids have a neutral PH and do not attract moisture like DOT 3 and DOT 4 fluids and is paint-safe if spilled. However, DOT 5 is not compatible with glycol-based DOT 3, DOT 4, or DOT 5.1 fluids, and will turn to gel if mixed. Wilwood does not recommend using silicone-based DOT 5 fluid in racing applications because it is prone to aeration and foaming under normal braking conditions, providing a spongy brake feel.
Whenever you add fresh fluid to your existing system, it immediately becomes contaminated, lowering the new fluid's boiling point. For maximum performance, use a high boiling point fluid and flush the system thoroughly. For street cars, flush and refill the fluid every year. For race or track driven cars it can be beneficial to change the fluid after every race weekend, especially after racing in the rain, severe temperature use, or brake fluid boiling.