ONAN Genset Raw Water Impeller Failure

[impi]

Hi fellow cruisers ... I need some assistance:

I have a 'new' Onan genset which Cummins / Onan are struggling to sort out under warranty.
The genset is an Onan 7/9 Kva model, has 440 hours and has it's 4th impeller set installed.
The impeller vanes break clean off ... last one only lasted some 50 hours.
The water pump">raw water pump is a Sherwood pump with impeller 2 1/4 inch diameter, part number 10077K (Sherwood) part no. 0132-0498 Cummins.
The impeller tolerances seem very tight to me ... but I am told this is normal?

I have checked the following:
- Strainer is clean.
- when the engine runs, water is in the strainer and pumping strongly.
- All hose clamps seem tight and no visible air leaks
- Raw water pump feels cool / cold when running
- Water hoses both on intake and exhaust side of pump feel 'relaxed' when running i.e. no buldging or stiffness which would indicate a restriction.
- Water runs well through the exhaust outlet to sea.
- when replacing the impeller, make sure it is lubricated with soap water for initial start up.

Cummins cannot assist me and just send emails back and forth ... no action taken.

Any ideas for me?

[s/v Jedi]

Sure, here's some:

- the water hose that carries water from the strainer to the pump. It should approach the pump from above, even when the connection is at the bottom of the pump. This makes sure that the impeller stays flooded when the genset isn't running, for a lubricated start next time.

- remove the impeller and check the housing, cog and inside of lid for any abrasions, burrs etc. If you find any, take care of the problem. The lid must be smooth.

- distrust the impellers you have. Go out and buy one from a different source and try that one.

- measure pump capacity by timing how long it takes to fill a bucket with exhaust water. Do the math to get to gpm or lpm and check that value with the manufacturer.

- If under warranty, ask for a replacement pump to see if that takes care of the problem.

ciao!
Nick.

[impi]

Hi Nick ... Nick to the rescue again ... thanks !

Yeah .. what you say does make sense. The 'face plate' / wear plate has now worn deep grooves into it ... the pump housing has 'chatter marks' in it ... the strainer sits at higher than the pump by at least 0.3 meters so although the strainer drains its water back to the ocean, there is water in the pipe between the strainer and pump.
Have not measured pump capacity yet ... will do that!
Have asked for a new pump.

Thanks

[Lagoon4us]

A bit of drift here, i've noticed on the ss raw water pipe that resides beneath the genset has a rubber hose connection at either end. These pipes corrode out i think because they are not electrically connected...ie a piece of wire also clamped externally bridging the metal parts to each other. Check if yours is same? Just an observation ....cheers

[impi]

Originally Posted by Lagoon4us

A bit of drift here, i've noticed on the ss raw water pipe that resides beneath the genset has a rubber hose connection at either end. These pipes corrode out i think because they are not electrically connected...ie a piece of wire also clamped externally bridging the metal parts to each other. Check if yours is same? Just an observation ....cheers

Ok ... I have not checked that one yet ... but should we have corrosion at 440 hours?

[Lagoon4us]

No way but just check it out whilst you are ferreting around there, if yours is same as ours then sort it while you are there, 1800 hours and 'Pearls' had electroylis in the tube causing a leak and those pipes are hard to get out......

[eeyore]

Hi

I have exactly the same problem. Same generator, same hours and 50 for the latest impeller. Did you solve yours and how?

Thanks

[Bradley]

I had the same experience with a 14 kwh Onan. I replaced the face plate and fine sanded the inside of the housing. This seems to have helped, but the generator is not being used much since the installation of 8 solar panels.

[impi]

Originally Posted by eeyore

Hi

I have exactly the same problem. Same generator, same hours and 50 for the latest impeller. Did you solve yours and how?

Thanks

Hi guys ... yes, we have managed to resolve the problem or rather, we are busy resolving the problem. We went to the boat show">Miami boat show and met with the Onan people who kindly replaced our pump with a new one, however, it seems Laggon have an install problem (heard this from a few people) in that the filter housing is installed too high. The water runs back to the sea and the on the next start up, it takes too long for the impellor to become lubricated. As a temporary measure, I soaked the impeller housing in corrosion X lubricant, which seems to penetrate metal, and in fact that has lengthened the life of this impellor.

I have been advised to install an electric pump similar to what the aircons use with same flow and rate and totally remove the raw water pump out of the circuit.

I have also been advised to remove the 'cooler' and clean it out as the broken rubber fins get trapped in the housing causing heat build up.

So yeah ... it seems one must do whatever it takes to get sea water to the pump as quickly as possible.

[Lagoon4us]

The reason they have given is logical however your boat is not hull number one?

1) Why has this problem not surfaced with every forerunner to yours unless there is some change as in previously there may have been a one way valve or a loop?

2) What i previously posted regarding electrically connecting each section of SS cooling tube where the rubber hoses join them together is of importance to prevent electrolysis in the future, i gotta tell you extracting the long SS raw water pipe that runs under the unit is not easy....
Frank

[s/v Jedi]

I post this info often: the raw water hose must be coming down to the raw water pump. This makes the pump a low point and water will stand there to lubricate impeller on next start.

cheers,
Nick.

[Lagoon4us]

Originally Posted by s/v Jedi

I post this info often: the raw water hose must be coming down to the raw water pump. This makes the pump a low point and water will stand there to lubricate impeller on next start.

cheers,
Nick.

Agreed they are called 'pumps' NOT 'sucks'.........

[twistedtree]

Originally Posted by s/v Jedi

I post this info often: the raw water hose must be coming down to the raw water pump. This makes the pump a low point and water will stand there to lubricate impeller on next start.

cheers,
Nick.

Only needed if the pump is above the water line, right? I imagine the pump and/or genset has a spec for the pump's level relative to the waterline to avoid such issues.

[dirkdig]

Mine went at about 400 hours so i replaced it.
During which i found about 4 impellors worth of fins in the heat exchanger downstream,got these out and water throughput increased.
So its rinning at an average of 100 hrs per breakdown.

[Lagoon4us]

What brand name is the pump? I remember Johnson having SIMILAR problems with a dodgy batch of impellors? ie are the impellors GENUINE?