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Old 07-04-2014, 09:46   #1
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ONAN MDKBH

I have a Cummins/Onan 5.0MDKBH. It is a nice generator, and I like it a lot, but it has one flaw. The water pump">raw water pump is at the top of the engine, which means that on our boat it is above the water line. On startup, it takes about 5 seconds for the pump to draw seawater up to it, which means that the rubber impeller is running dry for that time. As a result, we we are going thru 2 or 3 impellers a year with only about 75 hours of running. It is a big job replacing the impeller, since the whole pump must be removed. The engine is a Kubota Z402. The pump is a Sherwood 8000.

I am aware of the Globe run-dry impellers, but unfortunately they don't make a model for that engine.

Has anyone got any ideas how to resolve this problem. What are your thoughts on replacing the belt driven pump with an electric one placed below the waterline.
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Old 10-04-2014, 13:23   #2
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Re: ONAN MDKBH

We did exactly that with an AC driven pump by March on our Entec 4.2Kw genset. Pump and filter was below the waterline, as soon as the generator started producing AC power, it would power the pump. It's a good solution.. Kiss your chewed up impeller problems away.
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Old 10-04-2014, 13:49   #3
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Re: ONAN MDKBH

Thanks Neelie. That is exactly the kind of information I was looking for.
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Old 10-04-2014, 14:23   #4
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Re: ONAN MDKBH

Forgot to add that it was wired upstream of all the generator protection breakers. So if the gennie was overloaded and tripped the main breaker, the pump would still be powered. Pump circuit appropriately fused and protected of course!
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Old 10-04-2014, 14:59   #5
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Re: ONAN MDKBH

I just put a check valve in the intake line. I was only getting about 50 hours out of my impellers before I put it in. I got about 600 hours out of the first one and am approaching 400 hours on this one. Since I used to go through a lot of impellers I still have 3 or 4 spares on board. I got brass check valves from West marine. I was afraid they would not last long, being brass, so I have a spare on board, but I'm at about 1000 hours and the check valve is still going strong. Also the check valve is well above the water line so if it lets go I won't loose the boat.
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