An exhaust gas cooler assembly (10) with an internally located bypass tube (50), spaced apart from and disposed within a core passage (60), with an exhaust gas inlet manifold (40) directing exhaust gas to a plurality of cooling passages (52, 54, 56, 58) or to the bypass tube (50) by means of control valves (42, 44). Further provided is a detachable valve cartridge (84) with an actuator (16), with all moving components being included within the valve cartridge (84) and actuator (16).