Posted by Steve Dashew (September 7, 2001)
Water Pumps/Changing Impellers
One of the maintenance issues that is bound to occur is a bad salt water pump impeller.
The photo above is from Wind Horse‘s starboard engine. Notice the missing vane in the lower right portion of the impeller? It would have been better to change this impeller on a proactive basis, before it got old and tired. The missing vane reduces cooling water flow, and we now have to find the piece so it does not block one of the heat exchangers.
Each engine installation will have its own requirements for changing the impeller. It makes sense to go through this learning curve at the dock, where there is plenty of time and technical help is but a cell phone call away.
Regardless of the pump type and orientation, you are going to find that getting the new impeller installed can be a battle. The vanes need to be bent over, and they do not like this position.
We’ve found a couple of things which make the job easier. The first is to coat the impeller and the pump shaft with silicon grease. This will aid the insertion and initial rotations. The grease on the shaft may make removal later on easier as well.
The second trick is to compress the vanes with a wire tie. The tie is cut after the impeller has been started onto its shaft.
Impeller kits usually contain a new gasket. Odds are this gasket will have a specific orientation. There is often a wider portion where it runs over the “squash plate” inside the pump housing. You will want to make sure the gasket fits correctly.
There may also be a small piece that covers the end of the impeller.
Most engine manufacturers have a suggested replacement interval. Keeping a youthful impeller installed typically avoids problems. However, if you run the engine with a blocked strainer, and the impeller runs dry for a period of time, it probably makes sense to replace it.
