After countless hours of searching, I could not find the the oil specs recommended for the rv generator. I finally broke down and went to my local Cummins center, and bought the factory Onamax 15w-40. I say broke down, but honestly at $5.50/quart, i cant think of a reason to use anything else. But for anyone else looking for the specs, here they are:API Certifications - CJ-4, CI-4, CI-4 PLUS, CH-4, CG-4, OF-4, OF/SLAs I said, 15w-40 is what they said to use, which is part #326-5336 for a quart. A quick search of my standard go-to Mobil 1, showed it did not meet all the same specs.FYI- hope this helps.

Is it full synthetic? Because of the way splash lubrication works, I wouldn't use anything else, just because a small amount of oil has to do a lot of work.

mlts22 wrote:Is it full synthetic? Because of the way splash lubrication works, I wouldn't use anything else, just because a small amount of oil has to do a lot of work.Doesnt say synthetic on it anywhere, but it does say premium blend whatever that means. In talking to the service/parts managers, they said a couple things different in the Onamax is anti foam and anti splash. Either way, this one wont void the warranty, I gotta believe they stick their name on what they want in the equipment.

I use M1 Ow-40 in my 4K Onan, just because.

benb21601 wrote:After countless hours of searching, I could not find the the oil specs recommended for the rv generator. I finally broke down and went to my local Cummins center, and bought the factory Onamax 15w-40. I say broke down, but honestly at $5.50/quart, i cant think of a reason to use anything else. But for anyone else looking for the specs, here they are:API Certifications - CJ-4, CI-4, CI-4 PLUS, CH-4, CG-4, OF-4, OF/SLAs I said, 15w-40 is what they said to use, which is part #326-5336 for a quart. A quick search of my standard go-to Mobil 1, showed it did not meet all the same specs.FYI- hope this helps.FWIW, the specs that you list are diesel oil specs. Mobil 1 is for gas engines.

Cummins Onan Generator oil | Good Sam Community

BarneyS
Explorer III
May 11, 2016
Moved to Tech Issues from DIY.
mlts22
Explorer
May 11, 2016
Is it full synthetic? Because of the way splash lubrication works, I wouldn't use anything else, just because a small amount of oil has to do a lot of work.
benb21601
Explorer
May 11, 2016
mlts22 wrote:
Is it full synthetic? Because of the way splash lubrication works, I wouldn't use anything else, just because a small amount of oil has to do a lot of work.

Doesnt say synthetic on it anywhere, but it does say premium blend whatever that means. In talking to the service/parts managers, they said a couple things different in the Onamax is anti foam and anti splash. Either way, this one wont void the warranty, I gotta believe they stick their name on what they want in the equipment.
coolbreeze01
Explorer
May 11, 2016
I use M1 Ow-40 in my 4K Onan, just because.
haddy1
Explorer
May 12, 2016
benb21601 wrote:
After countless hours of searching, I could not find the the oil specs recommended for the rv generator. I finally broke down and went to my local Cummins center, and bought the factory Onamax 15w-40. I say broke down, but honestly at $5.50/quart, i cant think of a reason to use anything else. But for anyone else looking for the specs, here they are:

API Certifications - CJ-4, CI-4, CI-4 PLUS, CH-4, CG-4, OF-4, OF/SL

As I said, 15w-40 is what they said to use, which is part #326-5336 for a quart. A quick search of my standard go-to Mobil 1, showed it did not meet all the same specs.

FYI- hope this helps.

FWIW, the specs that you list are diesel oil specs. Mobil 1 is for gas engines.
Fleet_Man
Explorer
May 12, 2016
I use the same oil for both the Onan 8KW Quiet Diesel and the Cummins ISB-02 diesel in our MH. Same specs for both, why bother with another oil to buy or keep on hand.
Ductape
Explorer
May 12, 2016
I use 5w-40 Rotella syn. Available everywhere.
mchero
Explorer
May 12, 2016
Ductape wrote:
I use 5w-40 Rotella syn. Available everywhere.

X2
CharlesinGA
Explorer
May 12, 2016
Here you go, everything you need to know about your Onan generator.

http://power.cummins.com/sites/default/files/literature/rv/F-1123-EN.pdf

Charles
fj12ryder
Explorer III
May 13, 2016
I put the same stuff in it that I put in my big Cummins: Delvac 1300 15W-40. Heck, it will probably age out before I get enough hours to change it. :)

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