A dosing unit comprising: an electrically operated fluid injector, configured to receive a fluid at an input port and additionally configured to eject the fluid from a substantially tube-shaped output port responsive to an electrical signal received a control input terminal; a liquid-cooled housing having an interior cavity, sized and shaped to receive the electrically operated injector therein and surround the fluid injector in the cavity with engine coolant flowing through the cavity, engine coolant passing through cavity via an engine coolant input port and an engine coolant output port, the liquid-cooled housing having a substantially circular output orifice, sized, shaped and arranged to receive the output port of the fluid injector; a cover for the cavity, the cover comprising a pipe configured to carry fluid to the input port of the injector; a first weld, circumscribing the cover and joining the cover to the housing thermally and mechanically; and a second weld, joining said housing to the substantially tube-shaped output port of the fluid injector thermally and mechanically, the second weld circumscribing the output orifice of the housing and circumscribing the tube-shaped output port of the fluid injector, wherein the cavity has a lower portion, which surrounds and is adjacent to the tube-shaped output port of the fluid injector and through which engine coolant flows, wherein, at the lower portion of the cavity, the liquid cooled housing comprises an inwardly extending, substantially tube-shaped flange, which extends part way into the cavity and wherein the output port of the fluid injector is inside the inwardly extending substantially tubular flange, characterised in that, the liquid cooled housing comprises a sleeve portion extending axially along a major portion of the output port starting from the second weld away from the output orifice contacting the output port and the engine coolant on opposite sides. an electrically operated fluid injector, configured to receive a fluid at an input port and additionally configured to eject the fluid from a substantially tube-shaped output port responsive to an electrical signal received a control input terminal; a liquid-cooled housing having an interior cavity, sized and shaped to receive the electrically operated injector therein and surround the fluid injector in the cavity with engine coolant flowing through the cavity, engine coolant passing through cavity via an engine coolant input port and an engine coolant output port, the liquid-cooled housing having a substantially circular output orifice, sized, shaped and arranged to receive the output port of the fluid injector; a cover for the cavity, the cover comprising a pipe configured to carry fluid to the input port of the injector; a first weld, circumscribing the cover and joining the cover to the housing thermally and mechanically; and a second weld, joining said housing to the substantially tube-shaped output port of the fluid injector thermally and mechanically, the second weld circumscribing the output orifice of the housing and circumscribing the tube-shaped output port of the fluid injector, wherein the cavity has a lower portion, which surrounds and is adjacent to the tube-shaped output port of the fluid injector and through which engine coolant flows, wherein, at the lower portion of the cavity, the liquid cooled housing comprises an inwardly extending, substantially tube-shaped flange, which extends part way into the cavity and wherein the output port of the fluid injector is inside the inwardly extending substantially tubular flange, characterised in that, the liquid cooled housing comprises a sleeve portion extending axially along a major portion of the output port starting from the second weld away from the output orifice contacting the output port and the engine coolant on opposite sides.