A heated fuel injector includes a heated body, liquid fuel flowing through a fuel passage within the body, and a member that increases heat transfer from the heated body to the fuel within the fuel passage. The thermal efficiency of the fuel injector is increased separately or in combination by diverting the fuel flow along an inner circumferential contour of the heated body, by limiting the volume of fuel bypassing the heated inner surface of the body, by redirecting heat from the body to unheated portions of the fuel flow field within the fuel passage, and by increasing the available contact surface area for heat transfer. Improved heat transfer from the heated body to the fuel is achieved by integrating features that increase the contact surface area into the inside surface of the body or by positioning an insulating or a thermally conductive spacer within the fuel passage.