Brakes work by converting energy into heat. Some of this heat is absorbed by the brake fluid. If brake fluid boils, "vapor lock" will occur which means brake failure. Therefore, brake fluid must start with a high boiling point known as the "Dry" Boiling Point. But, brake fluid absorbs moisture from the air which, in time, lowers the boiling point and fluid performance. So, Lucas Girling Universal brake fluids have been developed to maintain performance for as long as possible (Click Graph Above). However, for maximum safety and braking performance, Lucas recommends that brake fluid be changed, at least, every two years.