Valvoline ™ Brake & Clutch Fluid DOT 5.1 is based on glycol ether, and has been developed for use in hydraulic brake systems. It is not harmful to any material in the brake system. The brake fluid is hygroscopic. That is, it attracts moisture. Therefore, the boiling point will decrease over time. It is recommended to change the brake fluid every year. Valvoline ™ Brake & Clutch Fluid DOT 5.1 can be mixed with other glycol ether-based fluids with corresponding specifications.