Abstract: An auxiliary power unit (APU) is provided and configured to be mounted in an APU compartment that defines an inlet opening. The APU includes a power section having components lubricated with oil; an intake duct coupled to the inlet opening and the power section and configured to direct a first portion of air flow through the inlet opening into the power section; an oil cooler coupled to the power section and configured to cool the oil of the power unit; a cooling duct coupled to the oil cooler and the intake opening; an inlet door mounted at the inlet opening and configured to open and close the inlet opening, the inlet door further configured to be positioned in at least a first open position and a second open position; and a thermal management system configured to adjust the inlet door between the first open position and the second open position based on one or more operating temperatures within the APU.