Evans Prep Fluid - Waterless Engine FlushMost new customers wanting to use Evans will need to remove the existing water based coolant from their system. To Gain the maximum benefit from Evans we recommend that no more than 3% residual water is present in the coolant. To help achieve this we have formulated a hygroscopic Prep Fluid designed to flush the system before adding Evans. How Does It Work? Fill the freshly drained cooling system with Evans Prep Fluid and run the engine up to normal