Usually the root cause is very simple! Annoyingly, it's usually NOT SIMPLE to find it!
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11-27-2017 11:17 AM #21Senior Member
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- Jun 2007
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Re: Onan MDJE Raw Water Pump Not Pushing Water/ Cure
FTFD... i drive a slow 1968 41c381
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Re: Onan MDJE Raw Water Pump Not Pushing Water/ Cure
This exact same problem happened to a friends trawler shortly before he died. He bought a new SS mixing elbow or shower (not sure which now) and I asked my mechanic to look at it before he did the install. Yep, it was a collapsed hose. They can be easily overlooked.
Bobk
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07-23-2020 09:07 AM #23
Re: Onan MDJE Raw Water Pump Not Pushing Water/ Cure
I'm hoping (for me anyway) that this gives final closure to this thread. So far I have replaced every component of the raw water cooling system and did phosphoric acid flush of heat exchanger. This included replacing the muffler, the exhaust hose (which had an inner liner tear), and new raw water pump a fellow member had as a spare. This all worked for about a season, then it came back. I would get it going again by disconnecting the output hose from pump and re-priming it by manually starting the generator with my finger over the heat exchanger raw water intake (it spits residual water back out from exhaust otherwise) and letting output hose run into the bilge, then stopping and reconnecting to heat exchanger. So last time I did this it would not do it first time around, which got me thinking maybe an intake air leak. I checked out the strainer and noticed the water level and that the output (intake to raw water pump) was only about half way. This is natural water level when boat at rest. So again I throw kitchen sink at it by completely rebuilding the strainer with new gaskets and proper wing nut (about $40 total) as well as turning it about 30 degrees so the input and output are now completely submerged. I also found a place that sells ‘New’ onan mdje water pump impellers (see below). I think the originals have been discontinued for some time (been buying spares on ebay) and that they perhaps even shrink over time? I noticed comparing old one to new one that the new one seemed just a few hairs wider. Anyway, rebuilt strainer as well as new impeller done at same time so can’t tell for sure what actually fixed it, but so far so good after 3 separate outings. Oh Lord, please let this be the end….at least for 2 seasons
Before 1.jpgAfter-1.jpgImpeller.jpgScott
1976 43DCFB ,Hull #428, “Exodus”
Long Island, NY
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08-04-2020 04:27 PM #24
Re: Onan MDJE Raw Water Pump Not Pushing Water/ Cure
Please clarify where this section of hose was located. Between the HE discharge & muffler?
Between the muffler and side hull discharge? I suspect, closer to the generator if it is an exhaust gas
deterioration issue.
I am getting good flow out of my raw water pump (disconnected) and no loss of prime. When I
reconnect the resulting overboard exhaust flow is a fraction of what the pump alone puts out.Ken C.
Comfort Zone
1978 42' Bertram FBMY
Sandusky, Ohio
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08-04-2020 04:51 PM #25
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08-05-2020 11:08 PM #26
Re: Onan MDJE Raw Water Pump Not Pushing Water/ Cure
It was the hose between the muffler and thru hull. Believe you are suppose to get that hose looping above the exhaust manifold for proper installation. This caused too tight a 180 degree bend in my hose and at about apex of loop is where the inner ply separated. Hope this helps.
Scott
1976 43DCFB ,Hull #428, “Exodus”
Long Island, NY
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Re: Onan MDJE Raw Water Pump Not Pushing Water/ Cure
This is an update to this thread, with 98% success rate, at this time.
Note: Spring 2020, I ordered from Onan/Cummins and installed a new Cover Plate (had wear) and Wear Plate at the back of the bore (some wear), plus new gasket and impeller; retained the cam, which seemed "true"..
I still had loss of prime with the new parts installed. See remarks on my shim installation below.
I am going to maintain that the mfgr of the Onan/Cummins brand of impeller is molding them undersized at their width. They are slightly narrower than the bore is deep.
This year, Spring 2020, I permanently installed my 1/32" copper shim at the back of the bore, so that I do not have to re-fit it, each time I pull the cover plate.
I have had good water flow each and every start this year, since installing my shim, plus new parts; no fails. One time only, while running the genset under way, I lost prime. Otherwise, I have good water flow at all times.
So if the impellers by Onan are from China, I believe their dimensional configurations are suspect and they are slightly too narrow.
My next effort is to try and source a Jabsco impeller, which will fit, both for dimensional comparisons, plus the Onan's are fragile with a limited life. As mentioned before, my Jabso toilet impellers are very durable.Last edited by spartonboat1; 08-14-2020 at 02:35 AM.
50 Years on the Great Lakes...
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Re: Onan MDJE Raw Water Pump Not Pushing Water/ Cure
Have you replaced the cam? Sorry if you mentioned that somewhere.
Semper Siesta
Robert Clarkson
ASLAN, 1983 55C #343
Charleston, SC
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Re: Onan MDJE Raw Water Pump Not Pushing Water/ Cure
Hello, you can try Onanparts.com for impellers. Some times they have them and worth a try. I agree with the limited life of generator impellers compared to others on boats.
Walt Hoover
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Re: Onan MDJE Raw Water Pump Not Pushing Water/ Cure
I have not yet replaced the "cam". But I intend to acquire a new one from Onan, as it is the only part, which I have not replaced with a new part. I will pull my shim out, although it has been working, install the new cam and run tests!
If my tests prove less than 100%, I will retain the new cam, but re-install my shim, which seems to be helping.
Also, others have mentioned loss of suction. I have vacuum gauge, so I will try to run some of those tests as well.Last edited by spartonboat1; 08-19-2020 at 12:49 AM.
50 Years on the Great Lakes...