Reverse Osmosis (R/O) is reported by Huff' to offer a high volume engine coolant recycling process with very significant purification capabilities. The higher productivity per investment dollar, in spite of the initial capital cost of the equipment, may present the best opportunity for a practicable commercial recycling method capable of producing coolant that compares favorably with new (virgin) coolant.A system described by Huff has, since its introduction in 1990, been re-invented and re-engineered to optimize both the quality and cost effectiveness of the process. This paper describes many of the technical obstacles in the evolution that had to be overcome, and reports the state-of-the-art in commercial reverse osmosis coolant recycling technology. Process improvements that affected coolant quality and productivity are recorded. Coolant recycled by this method was analyzed and subjected to standard ASTM test procedures for performance comparison a similarly formulated virgin coolant.