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Old 07-01-2012, 09:26 AM   #1
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Onan Question

Question for the seasoned Rvers out there...Running the Onan while driving. We just made out 1st extended trip - 27 days and 5K miles. With the recent heat issues in lots of the country we got pretty uncomfortable at times driving in our 04 Camelot. We would start the Onan from time to time & run ACs for short periods to cool down the MH and always about 20-30 minutes from a campground to get a jump on cooling down in the park. I am reluctant to run the Onan for long periods, although they are obviously designed to provide power for extended periods; it just seems like it invites issues. A friend says he starts his generator and turns on the ACs almost continuously while driving and another who says this is not good for the overall longevity of the unit. The fact that running the Onan will cost about .5 - 1 gallon of $4 deisel per hour aside (that cost is far outweighed by the comfort factor to us), what are the pros and cons of running the generator for extended periods of driving?

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Old 07-01-2012, 09:40 AM   #2
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Hi and welcome to the forum.

I think your first friend is right. Gennys need to be run. Letting them sit invites trouble. If you did a search on this topic I'd be willing to bet that more than half would reply that they either always or nearly always run the genny while traveling in hot weather.

We're pretty lucky in that our dash air seem to do a good job and we rarely run the genny while in motion.


Rick, Nancy, Peanut & Lola our Westie Dogs & Bailey the Sheltie.

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Old 07-01-2012, 10:06 AM   #3
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Onan generators are capable of running 10,000 hours if serviced regularly. That's regularly given as the expected operational time between overhauls. Control items can fail of course, but that's going to happen when it happens.

Run it and stay comfortable. Better for it, and better for your mood.
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Old 07-01-2012, 10:14 AM   #4
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.....RUN THAT GENERATOR !!!.... Those Onans run better and feel better the more ya use em. If you're traveling 6, 7 or 8+ hrs. in hot, sultry climates, use the darn thing.....after all, ya paid to have this feature in your coach. Might as well enjoy it.

Now, having said this, I might shut down the dash air conditioner while hauling UP high country mountain passes like the Bear Tooth North of Yellowstone, or, Wolf Creek Pass East of Pagosa Springs, Colo. etc., in order to keep the load on the engine less while pulling up-hill, but then again, if you're pulling over these kind of routes, it's likely pretty cool outside and ya won't need the dash air conditioners, nor even likely the overhead a/c units.

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Old 07-01-2012, 10:22 AM   #5
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I run mine for as long as I need it. You ain't gonna wear out that onan. When I was parking in ski resort parking lots I would sometimes run mine two or three days and never shut it down. The RV was 11 years old when I traded it and the onan was still running strong and proably the best part still working.
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Old 07-01-2012, 10:23 AM   #6
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FEMA runs their Onan generators for 20,000 hours continuous with only stops for routine service. They are built to run, not built to sit idle.

Until I got my dash A/C working this past winter while in Florida, I was using the roof-airs to keep the coach comfortable for almost 2 years while traveling. It was the only way I would drive.

The only point to be aware of when using the generator while traveling is to change the air filter in the generator more often than what is recommended. It will suck up the road dirt and grime faster while traveling versus when parked.

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Old 07-01-2012, 12:09 PM   #7
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thanks for the input from experience. Just had to get past the idea that running something continuously generally ain't good. we'll definately be more comfortable on our next journey where heat is an issue.
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Old 07-01-2012, 03:41 PM   #8
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Onan has said that if you are not putting atleast 6hrs a month under load on the generator then you might as well take it out and use the space for storage. OK maybe not all of that but you understand. Use it that's why you bought it.
The stator windings need to be clean to work properly and by using it you keep it cleaner than NOT using it. If it sits it varnishies up and doesen't put out like it should.
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Old 07-01-2012, 03:59 PM   #9
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Re - cost of running generator. On my MH with side radiator if the engine AC is selected, the big fan turns on 100% and MPG decreases about one MPG. That is actually more than 1/2 gal per hour.

Have a nice day - Darrel
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Old 07-01-2012, 06:49 PM   #10
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Run it!! You are not going to hurt anything. On a recent trip we ran ours almost the entire trip of 5000 miles. The only time we shut it down was when we were plugged in.
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Old 07-01-2012, 09:59 PM   #11
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I posted this on another similar thread. It is from a gasser's perspective but maybe you might find it reasonable for your diesel.

I refuse to suffer. LOL

OK...FACT...my 5.5kw Onan's published fuel burn is .9 gph at full load. My AC runs about 1/2 load if both compressors are in use putting my expected fuel burn closer to .5 or .6 gph

Working theory:

I've read that dash air reduces mpg by 1/2 or more mpg. So, if I drive 60 miles (at 60 mph) at 8 mpg I will use 7.5 gal with the dash are on and 8 gal with the gen/coach AC running. That means I will burn an extra .66 gal. That is practically a wash except I am not suffering.

Now, consider this. If you are fighting head winds or hills you now see your MPG go down. Let's assume it is a bad day and you are now muddling along at the same 60 mph but now are burning at 6.5 mpg and 6.0 mpg with dash air. The gals burned respectively are 9.23 & 10.0 and the gen/ac saves about .77 gal in an hour. Now you save a little bit of fuel by using the gen and coach air and don't suffer.

Now, finally, if you hit hills you will not be bleeding any HP off the engine. You should save fuel by the buckets, have more HP available for the climb, and stay cool at the same time. Here is an example. 20 min climb at 45 mph (15 miles) burning 4.5 mpg with dash and 4.0 without dash air. That is 3.33 gal vs 3.75 gals used. Dash used an extra .42 gal while gen used about .2 gal.

Even if the dash air only costs about .25 mpg you are near break even in most flat land, easy driving situations but motoring along with a cool environment. Any headwinds and/or hills quickly closes that small gap. I would also suspect that the tranny will not kick down as often in rolling terrain.

Hey...it's a working theory.

CAVEAT...diesel operators may have different opinions on the affects of dash air. Your mileage may vary, see own's operator manual for more information, my theory comes with no warranty implied or otherwise and always drive safe.
Don, Sandee & GSD Zeus. Guardian GSDs Gunny (7/11/15) & Thor (5/5/15)
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Old 07-02-2012, 09:09 AM   #12
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Summer or winter I run my Onan on (usually) the first trip every month, I either plug in heaters (winter) or run the A/C (Summer) Books says to run it 1/2 hour under 1/2 load every month and the easiest (Best in fact) time to do that is when going down the road.

This month is an exception as first trip was yesterday and I ran it for several hours within the last 2 weeks. Had a vision exam and such at Wal-Mart, so we pulled into the lot (over 90 degrees that day) hooked up the Gen-Turi and cranked it up to keep the kitties from melting. That was a couple of hours.. By that time the temps were high enough I kept it on till I got back to that lovely 50 amp hole in the box in the RV park

Home is where I park it!
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