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Old 03-13-2009, 08:51 PM   #29
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Old 03-13-2009, 08:52 PM   #30
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I learned the hard way on a 4KW Onan in our last 2002 Itasca about running the genset each month. I had let it set for about 4 months during the hot summer here in Phoenix and the results were varnished carb jets, bad fuel/filter, and a $100.00 plus bill to set things right again.

I now go by the book and run the genset for 30-45 minutes at half load or more each month. No more problem. The worst thing you can do for a genset is let it sit.

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Old 03-14-2009, 05:01 AM   #31
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More use is better. When staying somewhere for more than 30 days I put slides in and out, start generator and run it under load for 15 min. Of course I am in coach full time so no storage.
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Old 03-14-2009, 06:00 PM   #32
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I run my generator for an hour each month -- in the winter time load it with an electric heater and in the summer run the air. While the generator is running, I use that time to polish woodwork, clean leather, and any other inside chores that I have to do. If it is warm outside, I use the time to wash windows and any other small chores that I have been listing out on the "to do list."
Dave and Karen -- '02 Ultimate Advantage 36 C, 350 HP Cummins, Allison 3060 Tranny
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Old 03-24-2009, 09:06 AM   #33
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I spoke with a gentleman who ran generator maintenance in the Air Force for over 20 years and he said the same thing, 1/2 load for 30 min depending on the model. For Onan Quiet Diesel generators this should be increased to every 2-3 weeks. According to him you need to heat up the insulation on the wires to prevent mositure from building up, he says this is the number 1 reason for failures of this type of generator because they have an inverter and variable speed motors that are load dependant. With his level of expertise he should know, he also does seminars at a lot of conventions so that other RVers can benefit from all he has learned, I listened!
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Old 03-24-2009, 09:45 AM   #34
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I don't understand why a 10 or 12.5KW genny could be run with no load but a 7.5KW genny should be run under load. I thought the idea behind running under load was to place a load on the generator to dry any moisture from the windings and drive moisture from the oil. Plus it puts fresh fuel in the system. I might have misunderstood but I also wonder why it was indicated the smaller generators might not run at a constant speed.
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Old 03-24-2009, 05:19 PM   #35
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Why not just follow what your Onan manual says? The hearsay and "experts" posts above seems to drift from what the Onan manual says on this subject.

Get YOUR ONAN operator manuals at

According to the Onan operators manual for both the 10kw/12kw units (models HDKCA, HDKCB, yes, these are diesels, yes your different model genset may say something different), the section entitled "Exercising the Genset" specifically states run the (model HDKCA, HDKCB) genset at least 2 hours each month at 1/2 rated power if use is infrequent. It goes on to say - This drives off moisture, re-lubes the engine, replaces stale fuel and removes oxides from the electrical contacts. The result is better starting, more reliable operation, and longer engine life.

It seems in general Onan says 2hours run, every month at 1/2 power for everything based on their FAQ quoted below:

Further info from the ONAN web site http://www.cumminsonan.com/rv/support/faq/

Do diesel generators need exercising like gasoline generators?
Yes, regular exercise helps lubricate the seals and engine components and keeps carbon from building up. Regular exercise also heats up the generator windings and removes or expels excess moisture. In sets equipped with brushes, exercising helps prevent corrosion build up on the slip rings.
How often should I run my gasoline generator to keep it in good condition.
It may seem strange that not using a machine could cause performance problems, but with RV generators that's exactly the case. Regular "exercise" is an important part of keeping your generator healthy. Lack of use can cause moisture build-up and fuel system damage that makes it run poorly. In fact, in as little as 30 days, the fuel in gasoline-powered generators can begin to break down into gums and varnishes that clog the fuel system. Fuel varnishing results in hard starting and surging. (A surging generator never settles at a stable operating speed.)
To prevent such problems, we recommend running gasoline generators at a minimum of 50 percent capacity (for example, 2000 W, or one air conditioner for a 4000 W set) for two hours at least once every four weeks. A long two-hour exercise period is preferable to several short periods.
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Old 03-25-2009, 03:06 PM   #36
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At the FMCA International Rally in Pomona, CA in 2006 there were representatives from Kohler, Generac & Onan at a seminar on generators their recommendation was to exercise the generator a minimun of 1/2 hour twice a month under load, but preferably 1 hour twice a month under load.
Their description of "under load was turn on an air conditioner.
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Old 03-25-2009, 06:27 PM   #37
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Seems the memories of those reps (at least the Onan ones) almost completely goes against the Onan written word. For me, I'll take written over spoken. Of course, any exercise has got to be better than none!

BTW: I especially like the conflicting memory of those reps reagarding the written Onan comment from their web site of ""A long two-hour exercise period is preferable to several short periods.""

Lots of flavors of ice cream in this world!! As I eat my favorite flavor, I just read the labels...
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Old 03-27-2009, 01:03 PM   #38
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Originally Posted by Baby Bear View Post
How about that! Everyone is saying 1/2 Hr run time at at least 1/2 load. This has to be a first with so many agreeing on the same thing! We are making progress here!!!
On my smaller model 7.5K Onan, the operator's manual states "if the generator is used infrequently to run it at least 2 hours minimum under 1/2 load once a month"
I don't use my generator that often, even while using the MH, so I try and run it for an hour every few months.
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Old 03-27-2009, 01:33 PM   #39
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A big popular misconception on generators is by people thinking they will wear them out by running them and not have use of it when it is needed. Not operating a generator is the worst thing to do to one. I would rather see a maintained generator with high hours rather than one with low hours.

When we had a motorhome, we often ran the generator to run the A/C when on the road and not use the dash air. We were out enough that it seldom went more than 4 or 5 weeks that it was not run for some time. On the occassion that we did not go out for two months, I did not worry about the generator. Let it set longer and you need to be doing the monthly operations.

Just be sure and service it on schedule. Clean oil, and clean filters makes for a happy generator.


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