A heat exchanger system includes a core structure with an oil flow path configured to receive an oil flow. The heat exchanger system also includes a fuel flow path included in the core structure and configured to receive a fuel flow. The fuel flow path is coupled to the oil flow path to allow the fuel flow to receive heat from the oil flow in the oil flow path. Also, the heat exchanger system includes a supplemental airflow path defined at least partly by the core structure and configured to receive a supplemental airflow that receives heat from at least one of the oil flow and the fuel flow.