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

j-d
Explorer II
May 13, 2016
Page 26 of the manual Charles linked above.

Which type of oil (by service designation) is going to depend on the Generator being Diesel or Gasoline Fueled. That chart seems to recommend the same viscosity for both fuel types according to anticipated temperature. Says Synthetic is OK after break-in.

Interesting note about Air-Cooled Onan gennys: Best Summer Viscosity (32* to 100*) is Straight 30HD.
MEXICOWANDERER
Explorer
May 13, 2016
Rotella T is a batch oil

and far superior to plain Rotella oil in every single respect.
Chum_lee
Explorer
May 14, 2016
As previously mentioned 15W-40 weight oil is typically diesel engine lubricating oil and will meet the viscosity recommendations for almost any operating temperatures where you normally run your gas engine Onan genny. Although they are listed on the Onamax label, a lot of the specs that the OP listed are obsolete and have been superseded by more recent API specs/certifications which are generally backwards compatible. Onan's marketing and advertising department is just trying to confuse you and motivate you to spend more money on THEIR product. API CJ-4 and SM specs are current. Chevron DELO 400LE, Mobil Delvac, and Shell Rotella will all meet the specs Onan requires and typically cost about $12 to $14 for a 4 quart bottle. (less when on sale) Today I just went into Camping World and they want $11.95 for a quart Onamax genny 15W-40 oil. Aaaaahhh, no thank you. The above referenced products are widely available (Walmart, Costco, Kragen, Napa, Autozone, Oreilys, etc.) and, IMO the best deals in any town.

Onan manufacturers generators, they do not manufacture/blend oil. They simply buy bulk oil made by others that meets their specifacitions, repackage it in their proprietary containers and +-double/triple the price. If you prefer to buy Onamax oil or other $$$$$$$$ designer/boutique oils (synthetic) suit yourself.

Chum lee

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