A scroll expander was designed for an energy converter from waste heat of IC engine coolant to useful shaft work. The scroll expander is to run in a Rankine cycle which receives heat energy transferred from engine coolant circulation cycle. The working fluid was Ethanol. For axial compliance, a back pressure chamber was provided on the rear side of the orbiting scroll. Lubrication oil was delivered by a positive displacement type oil pump driven by the shaft rotation. Performance analysis on the scroll expander showed that the expander efficiency was 63.4%. It extracts shaft power of 0.6 kW out of engine coolant waste heat of 17.5 kW, resulting in the Rankine cycle efficiency of 3.43%.