Brake fluid is an essential part of the braking process when you depress the brake pedal, the fluid multiplies that pressure and transfers it to the wheels. As brake fluid ages it can absorb water from its surroundings. If this happens, when the brake fluid gets hot during braking the dissolved water will turn to vapour, giving a soft pedal feel and not allowing full transfer of the braking power. Its important that you change it at least every 2 years and make sure that youre using a fluid with a high boiling point. Prestone DOT 4 Brake Fluid has been developed using engineered technology to excel in high temperatures so that you can be sure it will perform for you on the road every day, while also protecting against corrosion.