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Old 06-21-2018, 10:14 AM   #1
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Join Date: May 2018
Location: south daytona
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onan generator oil change

about to do first oil change on onan generator (20 hours) on our Greyhawk. Information is extremely hard to try to get from anyone about oil. even owners manual does not address synthetic. I use Mobil 1 full synthetic in all of my vehicles, does anyone else use this of the correct viscosity (mine says 15w40) in your generators? Any stories, thanks.

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Old 06-21-2018, 10:17 AM   #2
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Might check with Cummins, Honda did not want us to use a synthetic!

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Old 06-21-2018, 04:24 PM   #3
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Look on the generator itself. I think IIRC I used straight 30w oil per manual .
'08 Greyhawk 31SS Traded in
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Old 06-21-2018, 05:31 PM   #4
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I use their OnaMax 15w-40 oil. That enclosed generator shoulders quite a load in hot weather to run the A/C. I figure that multi-weight oil might help it some.

2014 Greyhawk 31FK
2007 Honda Shadow Sabre 1100cc
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Old 06-22-2018, 09:20 PM   #5
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Mobil 1 15w40 in mine
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Old 06-23-2018, 05:02 AM   #6
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I use Rotella T4 15W-40 diesel oil. It is on the approved list for my Onan 5500 and since it is the same oil I use in my truck I only have to keep one type of oil on hand. 188,000 on the truck and 470 hours on the Onan and neither one has ever used any oil.


2006 GMC 2500HD CCSB 4x4 Duramax/Allison, Titan 52 gallon fuel tank, Prodigy Controller, B&W Companion Hitch
2010 Jayco Designer 35RLTS, Cummins/Onan RV QG 5500 EVAP, Progressive Industries EMS-PT50X, TST Systems 507 TPMS, RV Flex Armor Roof
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