For controlling temperature in the molding of plastics, metal, ceramic, or die-casting, a circulator supporting a molding machine includes a fixed displacement pump driven by an electronic servo motor for volumetric metering of thermal fluid to or from the molding machine. A pre-set or dynamically controlled volume and flow rate profile matches the heating and cooling requirement of a molding machine and process. Volumetric metering may be based on parameters such as time, machine cycle status, temperature, pressure, and/or flow rate. Fluid may be circulated through the mold at positive or negative pressure at fixed, variable, or pulsed flow. The supply side in a fluid loop may be restricted so as to cause a pressure drop in or upstream of the mold, die or barrel, and seed bubbles may be injected into the fluid flow to excite vaporization and lowering of the fluid temperature.