Rotary engines, by design, are somewhat more difficult to cool than conventional reciprocating powerplants. This arises in apart from the fact that all four cycles do not take place within the same physical portion of the engine. The basic aim of this research was to study the metal temperatures of many points in the rotary engine with standard and experimental coolants in an attempt to develop a product with superior heat rejection properties in a conventional cooling system.The engine used for the experiment was a two-rotor liquid-cooled Wankel engine obtained from a 1972 Mazda R-100. Both road and chassis dynamometer evaluations were run over a wide range of operating conditions to obtain a comprehensive look at coolant performance. The parameters studied for each coolant were road speed, engine load, coolant concentration, and ambient temperature; the coolants tested were ethylene glycol, water, and the experimental coolants XA-1318L and XA-1318.1L.Pure water was found to produce the lowest rotor housing metal temperatures under mild conditions of the four fluids tested; ethylene glycol produced metal housing temperatures above acceptable levels under severe test conditions. Both XA-1318L and XA-1318.1L reduced peak rotor housing metal temperatures compared to ethylene glycol, although XA-1318L appeared slightly inferior to XA-1318.1L. Under more severe test conditions, however, the two experimental brands of coolant were the most effective in reducing metal housing temperatures. It was concluded that XA-1318L or XA-1318.1L would be satisfactory coolants in a rotary engine.