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Old 11-25-2020, 01:13 AM   #1
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Brand: Thor Motor Coach
Model: Axis 25.3
State: Michigan
Posts: 44
THOR #20290
How much fuel does the Onan 4000 generator use in an hour?

DH wanted me to throw this question out there.

So far we have only needed to use our generator for short stints to recharge house batteries. (We also have a solar panel.) Consequently we have no idea how much fuel the generator would consume if, for example we were running it for an hour or more while boondocking.

Anyone ever monitor this and can give us some idea of what to expect?

We have a 2018 Axis 25.3, not that I think that would make a difference. We are pretty conservative when it comes to resource use (a throwback from our tent camping days); don't watch TV, enjoy the light of the campfire for the most part, early to bed, etc.

TIA.
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Old 11-25-2020, 01:25 AM   #2
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Model: 2018 24.1 AXISSIXxSIX
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THOR #13932
Half to three quarters gallon and hour.
It comes to about 90mpg if you're driving with the generator running.
Generator won't run if you're below 1/4 tank(ish) of fuel.
Aside:
Your v10 gets uses about point 67 gallons an hour at idle.
So running your dash ac while parked costs you 2 bucks(ish) an hour.
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Old 11-25-2020, 01:35 AM   #3
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I thought it was four-tenths of a gallon per hour.
But like me: my memory ain't what it used to be.
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Old 11-25-2020, 01:39 AM   #4
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Here's another number half gallon an hour when under load


Imo I dont worry about it. Its such a small amount. Run it when needed and don't stress

Jerry
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Old 11-25-2020, 02:05 AM   #5
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Fellow we camp by burns in that range close to full load and we burn about the same but at around 8-9k load, with the difference being the Diesel

Years ago I found if you ran a gas or propane generator flat out the fuel burn seemed to be on a significant upward curve so we tried to maintain around 75% load

They all cost quite bit to operate

Quote:
Originally Posted by Bob Denman View Post
I thought it was four-tenths of a gallon per hour.
But like me: my memory ain't what it used to be.
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Old 11-28-2020, 02:25 PM   #6
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Originally Posted by lwmcguire View Post
Fellow we camp by burns in that range close to full load and we burn about the same but at around 8-9k load, with the difference being the Diesel

Years ago I found if you ran a gas or propane generator flat out the fuel burn seemed to be on a significant upward curve so we tried to maintain around 75% load

They all cost quite bit to operate


At 75% load a 4000 KW per Cummins Onan fuel use is 4 /10ths of a gallon. Under full load 6/10ths . Not at all a gas user. Itís basically a lawn mower engine.
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Old 12-02-2020, 09:47 PM   #7
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FOR WHAT IT IS WORTH, THE MANUAL SAYS .3 gal/hr no load, 0.5 half LOAD, .7 full LOAD

Remember Onan says to operate the generator a minimum of 2 hours per month under load (air cond is our highest load).
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Old 12-02-2020, 10:47 PM   #8
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Originally Posted by aaurbanelli@aol.com View Post
FOR WHAT IT IS WORTH, THE MANUAL SAYS .3 gal/hr no load, 0.5 half LOAD, .7 full LOAD



Remember Onan says to operate the generator a minimum of 2 hours per month under load (air cond is our highest load).


Could never figure that one out. Manual different than statistical numbers published by Cummins on a 4000KW gas unit. Only talking tenths so I guess they donít care that manual different than chart published in 2017. Oh well nothing to fret over. The guzzler is the engine lol
Be safe and happy holidays
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Old 12-02-2020, 11:04 PM   #9
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I have a Vegas 27.7 with the 4000 gen.
I filled my tank to the very tip top. I stated the gen. drove 5 mile. Keep the gen. on for 20 hours ran A/C and lived just like I was home. Drove back 5 mile and filled up again. It worked out to .521 gallons per hour. If gas cost $2.00 per gal. you are staying for an over night stay, say 12 hours it cost you $12.48. Less that a $35.00-$45.00 per night at an RV campground. Love the Gen.
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Old 12-03-2020, 05:50 AM   #10
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Stopped worrying about it after our first night in a HH with no hookups. Ran our 8k for 13 hours and the fuel gauge didnít move. Continued to run for another 24, and the needle was still in the same place when we fired up the coach to continue the drive. I donít even take the generator into account when I figure where/when to stop for fuel, other than to make sure weíre always above 1/4 tank. Donít want the generator to shut off and have no roof A/C...-First World problems...
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Old 12-03-2020, 03:03 PM   #11
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Quote:
Originally Posted by Luke D View Post
The guzzler is the engine lol
Be safe and happy holidays
My. V10 uses 67/100ths of a gallon an hour at idle with the 3000w inverter and dash ac running.
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Old 12-07-2020, 03:14 AM   #12
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Originally Posted by Bob Denman View Post
I thought it was four-tenths of a gallon per hour.
But like me: my memory ain't what it used to be.
I'm told it will vary obviously between a half gallon to 3/4 gallon and hour because when A/C or micro is used it loads the genny!
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