Solution to Leaking Onan 20 fuel pump

[Bill Root]

A while back I made a post on the "parts wanted" a ection of the forum looking for a mechanical fuel pump for the Onan 20MDL generator on BUFFALO GAL. The original pump was leaking through the shaft and could not be repaired. As I soon found out, the fine folks at Onan Cummins decided to stop making that part about ten years ago. I searhed very possible lead for two weeks and came up empty handed. The generator has only 2500 hurs on it and runs just fine, so I didn'twant to replace it.

I received many recommendations from forum members on how to solve the leaking fuel pump problem, and I thank every one who offered advice. After discussion with my mechanic and a good marine electrician I had used in Ft. Lauderdale, I decided the best solution was to replace the old mechanical pump with an electric one. Of course, no one makes a 32V electric fuel pump any more, so we had to use a 24V pump. We took power from three of the 8V batteries in the house bank connected in series to produce the required 24V, and ran it through a solenoid that is activated by the generator starter switch. We did this installation last month and have used the boat several times since with no issues.

The only concern we had with the above solution was the impact it could have on the one battery in the bank that was not having power drawn from it. We still use the original equipment Lemarche charger, which I understand charges all batteries in the bank at the same rate. That means the battery that wasn't part of the 24V series would get charged right along with the others, which could potentially lead to overcharging of that one battery. The amperage draw of the fuel pump is so small, however, that we didn't feel it woul be an issue. I'll be monitoring that battery bank closely to see what actually happens.

This was not an inexpensive solution. What should have been a simple replacement of a $75 mechanical fuel pump turned into a fairly complicated project that cost over $500 in parts and labor, thanks to Onan's decision not to support their older model products. If I ever have to replace this generator, it sure won't be with an Onan.

 

[GJH]

Thanks for the update Bill. Having an MDL20 myself, it is interesting to me. Fortunately I have 2 24 volt banks (thruster and inverter) and a 12volt AGM (generator start) right there in my generator room.

I still maintain your beef is with Cummins, the engine manufacturer, not Onan. Onan uses a variety of engines today, made by many others as Cummins appears to have exited the small engine market.

 

[Avenger]

George, I think you may have missed that Cummins owns Onan and discontinued a lot of the Onan made engines when they took over.

 

[GJH]

I have the same generator as Bill. The engine on the MDL4 is a Cummins 4A2.3-M. It is not an Onan made engine. I have both the maintenance Manual and the parts manual... all Cummins.

 

[Avenger]

I believe it was a carry-over from Onan. If not it's very odd that the part numbers are Onan style numbers, and do not match Cummins number format. In any case, AFAIK the A engine is obsolete across the board.

Also, since Cummins and Onan are one company, it's hard to have a beef with one and not have a beef with the other.

 

[Avenger]

Here, I googled it for you:

The Onan L Series engine has had a short but troubled history. The Onan Corporation launched this water-cooled diesel shortly before the Cummins Engine Co purchased Onan in 1986. The Onan L Series was not widely adopted by equipment manufacturers. However this engine series was widely used in airport ground support equipment (i.e. GSE) such as airline baggage trucks, conveyors, and tugs. Shortly after Cummins bought the Onan Corporation they launched their B Series engine, which was offered in the same power and size category as the Onan L Series. Because of this overlap, Cummins then emphasized sales and support of their B Series and renamed the Onan L, the Cummins A Series. They then gradually withdrew parts and service support from the Cummins A Series engine.

 

[SKYCHENEY]

And if you want an old MDL4 for parts, I've got one.