This billet fitting from DHD will cap the EGR coolant passage port on LMM oil cooler coolant elbow. This plug is required when using the LMM elbow on earlier model Duramax engines that do not utilize this port. This cap is common for those running aftermarket headers & up-pipes. It can also be drilled and tapped to monitor cooling system pressure and/or temperature.
Note: Anytime you plug this port its required you supply coolant to the EGR cooler via another engine coolant port.