An external combustion engine having an exhaust flow diverter for directing the flow of an exhaust gas. The external combustion engine has a heater head having a plurality of heater tubes through which a working fluid is heated by conduction. The exhaust flow diverter is a cylinder disposed around the outside of the plurality of heater tubes and includes a plurality of openings through which the flow of exhaust gas may pass. The exhaust flow diverter directs the exhaust gas past the plurality of heater tubes. The external combustion engine may also include a plurality of flow diverter fins coupled to the plurality of heater tubes to direct the flow of the exhaust gas. The heater tubes may be U-shaped or helical coiled shaped.