Castrol React DOT 4 Low Temp brake fluid meets the new ISO 4925 Class 6 specification recommend by many vehicle manufacturers. Castrol React DOT 4 Low Temp is fully compatible with other fluids meeting FMVSS 116 DOT 3, DOT 4 and DOT 5.1. However, in order to maintain the superior performance characteristics of this fluid, avoid mixing with other brake fluid products. Advantages Castrol React DOT 4 Low Temp brake fluid not only exhibits excellent high temperature performance but is also formulated to provide improved low temperature performance. It has been specifically designed to have: Lower viscosity at low temperatures High wet boiling point Recommended by a number of vehicle manufacturers to assist with the speed and control of their electronic stability control systems (ESP and ABS). Hydraulic pressure generated in the brake system is used to apply the wheel brakes.