Here are some reasons why you may need to change the sea water pump on a Cummins engine:

1.      Wear and tear: Over time, the impeller and bearings of the sea water pump can wear down due to continuous use, leading to decreased pump performance and efficiency. Eventually, the pump may stop working altogether, which can cause engine overheating and other problems.

2.      Corrosion: Sea water pumps are exposed to saltwater, which can cause corrosion of the pump housing, impeller, and other components. Corrosion can cause leaks, reduced pump performance, and eventually, pump failure.

3.      Blockage: The sea water pump can become clogged with debris, sand, or other foreign objects, leading to reduced water flow and pump performance. If not addressed, the blockage can cause the pump to fail or the engine to overheat.

4.      Damage: The sea water pump can become damaged due to accidents, impact, or other causes, leading to decreased pump performance and efficiency. If the damage is severe, the pump may need to be replaced.

5.      Maintenance: Regular maintenance of the sea water pump can help identify issues before they become major problems. If the pump is found to be in poor condition during routine maintenance, it may be necessary to replace it to prevent engine damage.

In summary, sea water pumps are critical components of marine engines, and they need to be in good working order to prevent engine damage and overheating. Regular maintenance and timely repairs can help prevent issues that may require pump replacement.