An engine assembly (10) for an aircraft, including an internal combustion engine (12) having a liquid coolant system in fluid communication with a heat exchanger (66), an exhaust duct (70) in fluid communication with air passages (66b) of the heat exchanger (66), a fan (78) in fluid communication with the exhaust duct (70) for driving a cooling air flow through the air passages (66b) of the heat exchanger and into the exhaust duct (70), and an intermediate duct (80) in fluid communication with an exhaust of the engine (12) and having an outlet (82) positioned within the exhaust duct (70) downstream of the fan (78) and upstream of the outlet (72) of the exhaust duct (70). The outlet (82) of the intermediate duct (80) is spaced inwardly from a peripheral wall (70') of the exhaust duct (70). The engine assembly (10) may be configured as an auxiliary power unit.