Description Genuine coolant expansion/header tank for Cummins QSB 6.7 marine diesel engines. Cross References/Supersedes: 5305921, 529454500 Direct replacement OEM expansion tank for Cummins QSB 6.7 marine cooling systems. Designed to maintain correct coolant volume and pressure in closed-circuit engine cooling. Suitable for factory and repower installations where a remote header tank is required. Often paired with separate coolant expansion tank filler neck and O-ring seal 3028291, ordered separately.