05/22/2007 08:10:42 AM
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ted655
Admiral
Posts: 424
Joined: 02/09/2007
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Anyone have & use an onboard, water cooled genset? I need
advise on replacing the water pump impeller. Ours is a diesel Onan,
but any general knowledge is appreciated.
Thanks,
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05/22/2007 09:51:43 AM
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Coolbreeze
Member
Posts: 156
Joined: 07/16/2004
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Sure, got a water cooled Westerbeke and have changed it and on a couple dock neighbors Onans'. Fire away.
-------------------------
Rick
1994 Sumerset 80'
Lake Lanier, Ga.
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05/22/2007 11:46:15 AM
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houseboat8972
Admiral
Posts: 307
Joined: 05/05/2006
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When you replace the impellor, Flush out all of the lines leading to and from the pump, also checking the strainer for pieces of impellor. When installing the new impellor, squirt some dishwashing detergent around the blades before installing the cover. When you crank the generator it will lube the pump and also let you know if it is pumping well from the soapy water!
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05/22/2007 12:16:00 PM
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abdiver
Member
Posts: 168
Joined: 02/22/2007
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I had an Onan generator. Replacing the impeller was
essentially the same as replacing the ones on the main engines.
I didn't have to remove the pump, but it was awkward due to
the tight quarters the generator was tucked into.
Basically you need to remove the plate on the back of the pump,
reach in with a pair of pliers then work the impeller out (this is
a lot easier if the impeller is still intact.). There will probably
be a key on the shaft so be sure it doesn't fall out and get
lost.
To put the new impeller back in you want to lube it up with a
little vegetable oil or light grease (lithium or even vasoline
works well). Push the impeller up against the housing, give
it a twist (be sure to twist it the direction the engine will turn
it) to get the vanes to fold then slide it onto the shaft and into
the housing. A new gasket for the back plate is
recommended, so put it on and tighten the screws down and you are
all set.
Okay, that's the textbook answer.
Now, before you try all that get an old towel and spread it out
under where you are working to catch all the small parts you will
be likely to drop. Make sure you have turned off the sea cock
so you don't have water gushing in while you are doing this.
Get yourself a small mirror so you can peek around the
corners (unless you are lucky enough to have your generator sitting
out in a place where you can get around it.).
That answer your question?
Rod
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05/22/2007 02:04:18 PM
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ted655
Admiral
Posts: 424
Joined: 02/09/2007
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 Thanks!
I was just informed this morning that the generator ran only 10
minutes or so & then shuts down. The impeller is worn &
only "kinda" pumps. Once again, I'm not there, so how it sits &
how tight the space, I can't remember. I remember it down in the
engine hole & sits forward of the engine.
If just "worn", it should be intact. Lets hope the seacock works!
I'm going to put it on blocks to install the transducer so I cojld
install a new valve if needed.
I would have back flushed the system but may not have remembered to
clean the screen. I wouldn't have thought of detergent either. I
really had no idea of how big a job it might be. Hope I can still
get parts for the ol guy. Is it internal drive or belt drive?
I'm feeling better now, thanks everyone.
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05/22/2007 02:41:09 PM
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houseboat8972
Admiral
Posts: 307
Joined: 05/05/2006
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Impellors will be easy to find. West marine, BOAT US, etc all carry them, as do many local pump/machine shops. If it pumps now, but not good, try removing all of the petcocks from block and manifolds and run a pipe cleaner up in there and start the unit with those drain plugs out. You will be amazed at what comes out. Also clean out your sea-water strainer and make sure connections are tight. The least little blockage or air leak will change the pumps efficiency dramatically.
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05/22/2007 06:41:36 PM
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Pirate
Admin - super moderator group
Posts: 1346
Joined: 10/08/2002
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You can only get an onan impeller from an Onan dealer. The others will not work long.
-------------------------
The pirate
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05/22/2007 07:48:46 PM
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alreadygone
Admiral
Posts: 792
Joined: 02/07/2004
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If it only "kinda pumps" you can bet vanes are torn off. As already mentioned, but more indepth. Those vanes are still there somewhere!! find them. All must be accounted for, or they will restrict flow when new impeller is installed. Don't be suprised if there are more vane parts than impeller came with when new, because last replacer didn't get them all that time either.
Personally like vaseline over soap,,,,but then I've allways been a grease monkey.
Bob
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I carry a gun because it's too tiring carrying a cop.
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05/22/2007 07:59:44 PM
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mobay
Member
Posts: 29
Joined: 08/13/2004
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Ted,
Let me know how you make out with this project, I'm going through exactly the same thing. I have an Onan 6.5kw diesel generator on my Alcan and it too shuts off after about ten minutes due to overheating. I replaced the impeller last year and it helped somewhat, but I didn't know about all these other things to look for and check.
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-- Terry MasterCard III http://www.alcanboats.com/mastercard_iii.htm
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05/23/2007 07:48:12 AM
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ted655
Admiral
Posts: 424
Joined: 02/09/2007
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It's good to know to buy OEM, thanks. I'll be very diligent in
looking for "chunk". I hate the word assume (I always get in
trouble when I do it), so can I "hope" there is a discharge hose I
will be able to backflush thru? Are these vanes to be in the
pump cavity?
I will report back. It may take some time, as I doubt
there will be much wireless internet access along the way. We will
take a laptop. We will be working without you guys as a net for the
whole trip probably. Graduation day kinda.
Thanks,
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05/23/2007 10:07:42 AM
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houseboat8972
Admiral
Posts: 307
Joined: 05/05/2006
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Your sea-water pump WILL have a discharge line. Even if you find pieces in the pump housing, while you are at it, follow that discharge line which probably goes to a strainer. You will probably find more stuff in there. Best thing is to follow the path of all cooling lines and flush water back through them. The previous owner of my boat had never done this and the strainer was almost blocked from years of impellors, even the mechanic that I paid to change all impellors failed to flush the lines. It now pumps like a fire truck when it used to be a heavy trickle. And another "while you are at it" check the belt that turns the internal water pump and replace if necessary. It can go bad and cause the engine to overheat while everything else pumps like it is supposed to through the exhaust.
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05/24/2007 04:42:18 PM
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enginetamer
Member
Posts: 87
Joined: 02/14/2007
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Hi Mobay/ I fixed the problem you've described, on a customer's boat, by pulling out the fresh-water cooler and the oil cooler for servicing. The protective zinks had disintegrated and plugged up most of the long holes. Nothing wrong with the impeller. // Paul
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lookin' for adventure and the next wild engine!
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