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fuel tank installed for Onan 5500 gen


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We just purchased a 2015 Montana and plan to install an Onan 5500 gas generator in it. I don't want to use propane, so I want to install a 15gal aluminum fuel tank in the same compartment where the 12v battery is. Any issues with arrangement? Thanks for any input!


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Sparks and fumes don't play well together. If it were me I'd find another place for the tank or relocate the batteries.

Ray & Deb - Shelbi the Aussie & Lexington the cat
2004 Volvo 630 500HP ISX "Bertha D" - 10 Speed-MaxBrake -ET hitch.SOLD
2009 Designer 35RLSA SOLD
Fulltiming since '07 - stopped 2016

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I don't think that would be a wise idea Duane. Your batteries and any other electrical equipment in that compartment have the potential to arc/spark if shorted or during normal operation etc, this in combination with the right amount of vapor and oxygen would be catastrophic. I would refuse this if it came to my shop. What are the reasons that you don't want to use LP? Several considerations to keep in mind 1 LP give less wattage than gasoline the 6500 is actually a 7000 watt gas gen using LP 2 all generators will loose a percentage of output for every 1000ft above sea level. (See Onan site) That generator will burn approx .8gal/hr @ half load. 1.2gal/hr LP at high rpm no different than gasoline. You could add an LP connection to your current set up so that you could have a spare 40# tank (9.4 gallons) this combined with your existing 30# 7.1 gallon tanks that gives you around 23 gallons of fuel. I have 2 30# and made an adapter plumbed to the driver side tank with 2 40# cylinders for a total of 33gallons. If you do decide to go with LP whoever does the installation make sure they use the correct diameter of fuel type. Had a number of units come back from another shop doing an installation the unit would freeze up because they were using a small diameter fuel line.

I would highly highly suggest that you reconsider gasoline as an after market addition.

Edited by Walking thunder

2015 Cardinal 3850RL

F350 KingRanch using B&W Companion Hitch


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If you go to West Marine.com you can find all sorts of configurations and fill capacity of metal or plastic tanks. I went with plastic. I would keep the fuel supply system in a separate compartment or area. I put our 18 gal. tank beside the Marquise Gold 7000 separated by a metal wall. Also most of those tanks come with a fuel gauge sending unit in them. I bought a fuel gauge, wired it thru the 12 volt supplied for the hour meter and this set-up has served us well for 13 years of fulltiming.

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I for sure would not put in battery compartment. Stock on my 5er toy hauler the generator in the front and the fuel take in the back mounted under the 5er. I think there is a reason for it. They used fabricated metal angle brackets to mount to the 5er frame.


Ment to add mine is a gas onan 5500 also

Edited by Bob Cochran

2019 Thor Chateau 28E on a Ford E450 chassis. Maybe awhile but will get a new picture forgive one up there it is my old rig.

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  • 4 years later...

Well, it seems we have two conversations going......

As strongly advised above, don't put a gas tank near the batteries.  Just don't.  Our 2008 unit has a 5500 Onan Gold too, gas powered.  I doubt the first owners used it much, and we have put perhaps 40 hours on it in 5 years, most of that letting it run at the shop to exercise it and make sure it has fresh fuel.  If it's going to sit much, put in stabilizer, drain the tank, or both.  Ours is a toy hauler, so we have two stupid big tanks and a "refueling station".  I would rather have a propane unit and a couple 40# tanks to piggyback with the 2- 30# tanks, but it's what we got and it works.

As to the unit which won't start, check the ground at the generator.  Just because it's bolted to the frame means nothing.  Try running jumper cables to the starter solenoid.  If that starts it, just run a jumper from coach battery ground to the genny frame.  I'll bet dollars to do-nuts it's the ground.

Newmar X-Aire, VATICAN
Lots of old motorcycles, Moto Guzzi Griso and Spyder F3 currently in the front row
Young enough to play in the dirt as a retired farmer.
contact me at rickeieio@yahoo.com

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5 hours ago, bobsallyh said:

Lyndee, the amount of gas in the tank has nothing to do with the engine turning over. As far as fuel, I put Stabil Marine stabilizer in the tank when I fill it. You might want to check the voltage coming to the genny when trying to start it.

Thank you.

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  • 2 months later...

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