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Ethylene glycol based engine coolants are increasingly being judged as hazardous wastes. Across the USA, states are beginning to disallow these materials in their sewage systems (1)*. Various methods are being used to allow reuse of these coolant materials. Purification by vacuum distillation is one process that produces a very pure ethylene glycol for reuse. This paper describes the physical chemistry of the vacuum distillation process as it applies to an aqueous solution of ethylene glycol contaminated by a multitude of dissolved and insoluble solids. It summarizes data that shows the resultant ethylene glycol is of excellent quality for producing stable and protective engine coolant. The science of distillation has been used for centuries for purifying volatile materials; in recent decades, distillation processes have been developed that result in extremely high levels of purification.