Raw Water Pump Impeller
Why the Impeller is Vital to a Diesel Engine
The rubber impeller pushes water through the engine's cooling system. The engine will quickly overheat (and have to be shut down) if the rubber/nitrile impeller inside the raw water pump fails; so it's important to be sure the impeller is in good condition.
Impellers may be made of three different materials:
• neoprene - for clean sea or fresh water
• nitrile - more resistant to oil
• composite - survive longer if run dry, but may swell if immersed in some types of anti-freeze.
Six Faults to Find in a Rubber Impeller
These six faults can cause an impeller to fail suddenly. An impeller must be removed from the pump to inspect it correctly - the faults may well be invisible when the impeller is compressed inside the pump.
Best practice is to replace the impeller if any of these faults are discovered - before the impeller fails, causing the engine to overheat.
Search for any pieces or a whole missing vane because they can block the flow of cooling water through the system.
Common places to find rubber pieces are: 1) inside the heat exchanger, 2) inside the raw water injection elbow on the exhaust.
Always carry on board at least one spare impeller - fit a new spare in the pump, to be sure it fits, and keep the other as the extra.
