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Old 10-30-2020, 08:22 PM   #1
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Onan Genset Won't pump raw water

1990 Onan with 202M11 raw water pump. Quit pushing water. New impeller, old was torn, not wrecked. New impeller, will not lift water to the pump. Sea cock is clean, new hose on intake and raw water system last year. Clamps tight. I can see the impeller moving around with both discharge ant intake hoses off. No instructions. Back filled the system from the exhaust cooling hose to prime it (although the lift is less than a foot) nada. She will not pull water.
Sounds like an air leak and we've run it all summer with zero issues. Can the pump housing be cracked, allowing air? Baffled.
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Old 10-30-2020, 08:46 PM   #2
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One of the things I do after working on the water pump, is to remove the highest hose on the pump and fill the pump with water. I let it sit for a while and then top it up before reinstalling the hose. I find the pump seals better with a wet impeller, especially if there is significant lift to from sea level to the pump.

Ted
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Old 10-30-2020, 08:50 PM   #3
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Try pulling the hose off of the seacock and raise the hose above the deck level. Fill the hose with water from a dockside water connection to prime the pump. Start the generator and check for water flow and if established, shut down and connect the hose to the seacock. Restart and verify flow.

James
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Old 10-31-2020, 08:25 PM   #4
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Have you checked the impeller pump housing for wear?
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Old 10-31-2020, 09:14 PM   #5
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Is it a Globe run dry impeller (the blue ones)? I've tried those on several different engines, not one of them worked. Switched back to the black neoprene type, the pumps all worked fine. Something about the rubber compound in the blue ones causes them not to seal. They might work in a brand new pump, but not in one with some wear on it.
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Old 11-01-2020, 02:15 AM   #6
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The old way is to grease the housing and inside cover with waterproof grease. The grease helps seal the impeller to the housing and greatly increases suction. It also protect the impeller ends from getting too hot while waiting for the water. Once too hot, the ends become hard and don't work as well.
I pull my impellers once or twice a year and regrease the housing. If they don't have cracks or hard ends, I put them back in. I get about 500 hours out of my impellers. 2 Detroits, and Onan and Perkins.
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Old 11-01-2020, 07:33 AM   #7
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Could be pieces of the old impeller blocking the cooler. Blow backwards with your mouth. Collect the pieces, you will be impressed quantity of rubber pieces.
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Old 11-01-2020, 07:34 AM   #8
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A few times I bought new impellers for Onans and other engines that would not prime. Measured new impeller with dial calipers and found the new one was shorter than the old one!! Not by much (maybe 0.010") but that was enough for a leak path past impeller. I could tell this by blowing through pump with impeller installed. Could blow right through it. Sourced an impeller from another vendor (calipers in hand) and found one with the right length. Pump then worked.

Note that lots of Onan/Kubota pumps are driven by injection pump that only runs 900 rpm. Makes priming more critical.

If cover plate is worn, that will make it worse. Cover plate can be re-surfaced on a lathe or mill to get it back to being flat.

If whole pump is worn, may be a new pump in your future.

Best test is to blow through pump and see how much air goes through. Healthy pump only a little air will go through.
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Old 11-01-2020, 07:58 AM   #9
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I do hope you bought a couple of the correct impellers.
Cover plates can be turned over.
Lathe or mill time costs more than just buying a new cover.
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Old 11-01-2020, 11:07 AM   #10
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Quote:
Originally Posted by MacPhid View Post
Try pulling the hose off of the seacock and raise the hose above the deck level. Fill the hose with water from a dockside water connection to prime the pump. Start the generator and check for water flow and if established, shut down and connect the hose to the seacock. Restart and verify flow.

James
Good suggestion. However if you can, lower the hose below waterline and turn on the sea cock. You should have a lot of water. Now proceed with the above.

I have in the past had the intake plugged with kelp. So trace your water flow starting with the seacock.
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Old 11-01-2020, 04:53 PM   #11
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Wow. Some great answers! Done all of the above. Yeah, the blue impellers suck. My macerator ate one in less than a dozen cycles.

Pulled the Onan pump (this should be an Olympic event) and I'm finding a badly worn face plate. And even though the impeller is a perfect match to one that worked, it seems a tad loose in the casting at the fully extended part. No pumps on-line. The impeller does not extend out of the casting. It's dead even. May have to find a machine shop and at least get the wear plate to cozy up with the impeller.

Thank you all!
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Old 11-01-2020, 07:05 PM   #12
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Quote:
Originally Posted by NightCrawler View Post
Wow. Some great answers! Done all of the above. Yeah, the blue impellers suck. My macerator ate one in less than a dozen cycles.

Pulled the Onan pump (this should be an Olympic event) and I'm finding a badly worn face plate. And even though the impeller is a perfect match to one that worked, it seems a tad loose in the casting at the fully extended part. No pumps on-line. The impeller does not extend out of the casting. It's dead even. May have to find a machine shop and at least get the wear plate to cozy up with the impeller.

Thank you all!
Try here:

http://m.depcopump.com/?url=http%3A%...le.com%2F#3033
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Old 11-01-2020, 07:08 PM   #13
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May have to find a machine shop and at least get the wear plate to cozy up with the impeller.
Thank you all!
Turn the face plate over. Put the outside facing into the pump.
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Old 11-01-2020, 09:18 PM   #14
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Turn the face plate over. Put the outside facing into the pump.
Some pumps have an oring seal in the face plate to prevent that.

Lot to be said for having a spare pump and rebuilding the other at a time and place of your choosing.

Ted
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Old 11-01-2020, 10:20 PM   #15
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Had the same happen to the sherwood pump on our genset after I changed an impeller.
Location of pump was a blood letting event every time so removed the pump and blanked of the hole.
Installed an MD30 240v electric pump at an easy accessible spot and that's working better than ever , no impellers to wear out and no more blood letting.
Got near 1000 hours on it now,

https://www.ebay.com.au/itm/MD-30-Ma...wAAOSwKb5amlAE
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Old 11-03-2020, 07:10 AM   #16
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Quote:
Originally Posted by Simi 60 View Post
Had the same happen to the sherwood pump on our genset after I changed an impeller.
Location of pump was a blood letting event every time so removed the pump and blanked of the hole.
Installed an MD30 240v electric pump at an easy accessible spot and that's working better than ever , no impellers to wear out and no more blood letting.
Got near 1000 hours on it now,

https://www.ebay.com.au/itm/MD-30-Ma...wAAOSwKb5amlAE
Seriously considered this. The existing pump is rated 11gpm. Is the fish tank pump near those numbers.

Did finally have luck finding a new pump. Local team at Specialized Mechanical Services in Wilmington scored one. Should be here today.
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Old 11-03-2020, 02:51 PM   #17
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Seriously considered this. The existing pump is rated 11gpm. Is the fish tank pump near those numbers.
Our gennie spins @ 1500rpm so puts out less

They do make larger models, md40 , md55, md70
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Old 11-04-2020, 11:13 AM   #18
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Quote:
Originally Posted by NightCrawler View Post
Wow. Some great answers! Done all of the above. Yeah, the blue impellers suck. My macerator ate one in less than a dozen cycles.

Pulled the Onan pump (this should be an Olympic event) and I'm finding a badly worn face plate. And even though the impeller is a perfect match to one that worked, it seems a tad loose in the casting at the fully extended part. No pumps on-line. The impeller does not extend out of the casting. It's dead even. May have to find a machine shop and at least get the wear plate to cozy up with the impeller.

Thank you all!
Can you flip the face plate over and provide a NEW surface to mate with the impeller. This, along with greasing the mating surface, sometimes makes the difference.
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Old 11-06-2020, 02:23 PM   #19
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Our 1989 Onan Genst developed the same problem.....midway through a Medd cruise! A new impeller did not resolve the issue, and our faceplate showed considerable wear. We ended up ordering a new pump, and it's worked perfectly since(7 years now). I've read several blogs on this issue, and the idea of a stand-alone 230vAC pump, powered by the genset once up to speed, or a 12vDC pump on a separate switch, sound like really good advice. It's on our list of things to do, but for now.....if it ain't broke, don't fix it!
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Old 11-08-2020, 03:31 PM   #20
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Connected with Specialized Mechanical Services
http://specializedmechanical.com/
In Wilmington NC. Had a new pump overnight. Awesome service!!! She's working great!
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