A pumped loop heat transfer system which also stores energy by means of freezing part of the heat transfer liquid. A combination of immiscible liquids is used as the heat transfer fluid in a pumped system with heat exchangers at both the heat sink and the heat source. The liquids have different enough freezing points so that one will solidify in advance of the others, and the liquids are selected for the heat transfer application so that one liquid always remains in the liquid state. The freezing of one component at the heat sink helps to assure the other components will remain liquid, and the remaining liquid prevents expansion related stress and destruction and provides for easy startup of the system, since it begins heat transfer immediately, and its circulation past the frozen component quickly liquifies the solid.