This paper describes the properties of an engine coolant that uses a potassium propionate solution as base fluid. Although alternatives for ethylene glycol are known, e.g. propylene glycol and glycerin, the use of a salt based coolant for high temperature applications has seldom been considered as a viable option due to the intrinsic corrosiveness of such salt solutions. The salt based coolant offers freezing as well as boiling protection and has thermal properties that allow for usage in standard combustion engines. Volumetric heat capacity and viscosity are very similar to glycol based analogues, while its thermal conductive is substantially higher. Thermal experiments indicate that the potassium propionate coolant is highly effective in suppressing localized boiling phenomena. Due to its chemical nature the coolant has superior oxidation stability. The coolant has the further advantage of being readily biodegradable and has a low toxicity. The coolant contains additionally a tailored additive package that provides corrosion protection for the metallic parts of an engine cooling system. Although current industrial standards cannot be claimed because of compositional requirements imposed by them, laboratory testing has shown that the salt based coolant offers acceptable to excellent results in recognized industrial tests as ASTM D1384, ASTM D4340, ASTM D2570 and ASTM D2809. Similar good results were obtained in the cylinder liner cavitation test (ASTM D7583) indicating that both automotive as well as heavy duty applications are possible. Finally the paper will represent the results obtained in a limited mixed automotive - heavy duty fleet test.