Onan MDJA, 3KGenset

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grahamdouglass

Senior Member
Joined
Nov 29, 2012
Messages
413
Location
Canada
Vessel Name
Summer Wind 1
Vessel Make
Marine Trader 41
The seal went on the raw water pump. Cummins may not have the part.

I'm not ready to spend $10,000 on a new genset. Or mabey i'm too cheap.

Has any one retro fitted an electric pump to replace a gear driven pump on an old Onan genset?

I hear you wire it through the oil pressure circut so the pump comes on when the oil pressure is reached.

What make of elecric pump would you use? Any pictures or advice out there?
 
Contact Depco Pump in Clearwater Florida. They might have the part or can almost surely rebuild the pump,
 
If Howard's contact doesn't work and If you have a part number, try these folks. I have bought a lot of my parts for my genny. You will have to wait about 10 days to get the part.

https://www.jackssmallengines.com/
 
I replaced my raw water pump (Onan MDJE 7.5KW) with a standard air conditioner raw water pump. Wired into the generator side so it comes on whenever the generator is running.

Totally solved my belt-driven raw water pump problems. Each startup of the genset used to include a nervous walk to the stern to see if water was coming out with the exhaust. I still check, but now it's with a smile. I may even linger a while to enjoy the relaxing splash, knowing I don't have to do any vodoo to get the water flowing any more.
 
I picked up a 500 gph pond pump, 120v for $80

Hey Captn Tom, I picked up a 500 gph pond pump for $80 at Lowes. I didn't realize how cheap it was till I opened the package. I guess I'll see how it works when I put every thing together. I generally only run my genset in the morning to charge the batteries, heat up my shower and make my coffee.

The question I have is BACKFEED from the inverter when your at anchor. The way my system is set up, is when ever I have a draw and no external source the inverter will kick in. When the AC circut is not connected to the generator there is no connection at all and no draw. But as soon as the switch is made the pump will be looking for power. Therefore you could only turn the selector switch to generator after the genset is running and you would have to shut the genset off after you deselect the generator.

If you have a set up similar to mine have you ever selected the genset before starting the genset and have the pump come on and flood the cylinder?

Now, I haven't personally checked my connections at the genset to see if this is true and I will be doing that in the next couple of days but with my limited electrical knowledge I have been wondering about this backfeed question.
 
My inverter can never backfeed my genset. The inverter will switch between sources, not connect them. And my pump is not wired to a circuit served by the inverter anyway.

I actually found where the power came out from the generators side, and connected the pump to those terminals inside the genset control box. Any time the generator is producing power, the pump is on. When it's not generating, no pump. No way to flood the engine, and no impeller to burn up if the pump loses its prime or otherwise takes too long to start moving water.

I'd question how well a fresh-water pump would work in salt water. The March (or similar) raw water pumps are pretty rugged. Non-corrosive parts and no common shaft between motor and pump. Only down side is they aren't self-priming so they need to be below the waterline, and even then can lose their prime if too much air gets up into the lines. I always verify cooling flow after starting the genset. Again, with no impeller there's no risk in running for a few minutes with no flow. I would have time to open the sea strainer to release any air and get the pump primed, without even shutting down the genset.
 
Just be certain that the electric pump cannot run without the gennny engine running or it will flood the engine.

I second depco pump. They can fix yur pump.
 
An update on the genset fix. I didn’t use the cheap pump I bought, instead I already had a 120 volt 360 gph utility pump that always worked and never gave me any issues and pumped everything and anything over the last couple of years.

So, I wired a duplex receptacle to the genset terminal box, which I’ll plug the pump into and plumbed the pump to bypass the existing raw water pump. Works like a charm.
 
Thanks for the reply

I contacted an employee of Power West in the Vancouver area. Power West is a commercial firm that deals in generators and has been for the last 30 or so years. The fellow I talked to was familiar with the Onan MDJA.

I asked him about the seal inboard of the impeller on the raw water pump for the MDJA. They no longer make the seal kit or the seal on this water pump and I was hopping they might have an unused seal kit in their inventory.

He said he knows of no replacement for this part. And if the OEM is no longer made the pump is unfixable.

For now I have a fix, in terms of an electric pump. This winter I might take the old pump apart and have a close look at it, I'll check out the seal on the MCCK.
 
I recognize this thread is now six years old but
did you fix the ONAN? I have the fix for you, read on.
I have an MDJA and have re fit the seal
Its a std 1/2" mechanical seal MECHSGP-12177 it says on the box
from neseal.com in Burnaby
BUT
you have to reduce the OD of the tin cup to fit the ONAN housing.
the jist
they sent me a 3/8 one that fits the housing but not the shaft
so I got the one that fits the shaft (.500 instead of .375) and reduced the OD of tin cup to the 3/8 OD which then fits..
its just the flange that has to be reduced. I had my machinist do it but one could hack their way to success.

The shaft and bearings are made of unobtanium and run $500 IF you can find one
So, I had two made
by machinist, cost me about $300 each w/ initial bearing shaft cost and the machining.

I dealt w/ the old BC Bearing co now T-Mar in Campbell River to get the pieces.
The shaft is Part # BRG885586-NSK which is a bearing, integral shaft 5/8" a pretty common water pump shaft one machines to fit.
I also had end caps made and I found some SS washers that are quite similar dimension to the backing plate sans the notch which I figure I can hack in.

That said
the end caps, impellors, gaskets and inner plate are all available currently on ebay out of Florida

and as someone else said you have to reuse the ceramic washer. T-Mar did send mine down to a bearing hut in lower mainland and they 'renewed' it.. tonights its soaking in a low % Muriatic acid.

There are rebuilt pumps available now $1000...
ebay.

Cheers!
 
FWIW I finally deep sixed the proprietary raw water pump for all the above reasons. I put a simple Jabsco on the deck that holds the belt driven coolant pump. Im still on the same impellar after six years. Im thining about replacing that :). You adjust the tension on the new belt you will need by sliding the coolant pump. I used a 4 inch pully on the Jabsco. It feels good to beat the man:) I can send a pic if you email me.

Cheers
 

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