Abstract: Cleanup systems include plural coolant inputs that are physically combined to create a single flow at a desired filtering temperature. Filter(s) are used to clean the coolant, and coolant flowing therethrough will damage the filter or not be adequately filtered if having temperature in excess of an operating temperature of the filter. The inputs have different temperatures, and mixing them creates a combined flow at a desired temperature. The amount of each flow is selected based on its individual temperature to achieve this desired temperature. The combined flow is then conditioned with the filter at an operable temperature and returned to the coolant origin for the inputs. No heat exchangers or heat loss to outside heat sinks are required. Cleanup systems may be used with any coolant loop, including Rankine-cycle electricity generation systems like nuclear power plants, combustion boilers, and steam generators, and heat transfer systems.