Seawater Pump - erratic output - Hunter 38

[tvicknair]

Hi,

On our 2006 Hunter 38 with a Yanmar engine, the impeller disintegrated. After replacement of the impeller we only get erratic amounts of water splashing out of the exhaust. Sometimes it runs completely dry. We theorize that parts or a part of the disintegrated impeller are occasionally blocking the water's passage through the heat exchanger or the piping thereafter, perhaps even the check valve just prior to the exhaust. We hope that the design of the cooling system takes into account impellers disintegrating, but no idea if that is true.

Any ideas would be greatly appreciated, as we deeply wish to avoid removing and purging the heat exchanger.

All the best.

 

[Don S/V ILLusion]

Sorry to say that's why routine replacement of the impeller is an essential step. No doubt parts of the impeller are blocking the cooling system which needs to cleared. No other option exists.

 

[Rich Stidger]

On occasion I have had an impeller break up in my generator and often the largest parts are in the immediate pump input and output connections. I have been able to remove these parts with some stiff wire. It is very important that all the impeller pieces be located. Pieces can actually be pushed backwards into the input of the pump and then when these pieces come loose they will destroy the new impeller.

Regarding the heat exchanger, I had occasion to open my generator unit and I did clean out several pieces of impeller along with sacrificial zinc pieces. They were all caught in the end and did not get into the cooling tubes. I suspect that this is the most likely situation and these pieces of impeller don't seem to do any significant harm. Certainly not as you describe with fluctuating water flow.

I would pull out the new impeller, inspect it carefully for cracks/missing pieces, and look into the input and outlet of the pump. You likely will need to remove the attached hoses to the pump to effect a good cleanout.

 

[Bob 04 H260]

I have reverse flushed the heat exchanger on my generator as well as my Yanmar.

I flushed out some bits of rubber impeller and some sand on the generator. I used the fresh water hose at the dock. I also ran the water hose through the intake seacock for the raw water.

Once I reverse flushed the freshwater side of the engine cooling too. I didn't have any overheating problems. The engine was 10 years old, So I replaced all the engine hoses and I wanted to be sure it was all cleaned out.

Bob

 

[tvicknair]

Resolution. I did high a mechanic to help. Took of the cap to the exchanger on the aft side of the engine, which served as hose junction for both the fresh intake and output. Removed what appeared to be two or three impellers on the input side side of the cap. The impeller parts were blocked from going into the exchanger by the small holes on a plate. You will need a new gasket most likely. Now water flow is better than ever..

 

[markwbird]

Check the belt. Erratic implies sometimes on sometimes off. That sounds like a loose belt.