Just doing a service on my generator (5500 Marquis model 5.5HGJAB-1038D). Bought plugs and filter, but they wanted $15 a quart for the Onan SAE 15W-40. Thought maybe I could just get it cheaper at an auto parts store and not have to get the Onan brand.I noticed I have an open bottle of OnaMax SAE 30 in my garage which was probably for my old 4K generator.Question is can I use an oil other than Onan? I don't feel like driving all the way back to Camping World to buy 2 quarts, but will if that is what I should use.Auto parts store did not have non detergent 15W-40, but hat 30W. They do have 15W-40 that is not detergent free. I don't known if that even makes a difference.Thanks

I have been using a good quality oil for years, with no trouble. I think changing it at least once per year with the filter, and run it loaded once a month, will give you the best service.

You do not want non-detergent oil in an engine, the detergents break down the combustion byproducts and keep them suspended. Save it for the pressure washer pump. It also does not come as a multi weight,any of those will be a detergent type. Any 15-40 will be just fine as long as it is the correct weight and meets the specified API service classification. The OEM's make big money rebranding oil as you have discovered.

Interesting, when I asked the guy at Camping World what was so special about Onan oil, he told me it was non-detergent.I was going to go with Rotella 15W-40.

I use 15w-40 delo in my generator

Some Onan oil is SAE 10W40.Some is straight 30 weight.Any good quality oil will work. I use Castrol 15W40I do dot see why you Rotella should work.

Whats so special about Onan generator oil | Good Sam Community

Vet_Man
Explorer
Nov 08, 2014
I have been using a good quality oil for years, with no trouble. I think changing it at least once per year with the filter, and run it loaded once a month, will give you the best service.
romore
Explorer II
Nov 08, 2014
You do not want non-detergent oil in an engine, the detergents break down the combustion byproducts and keep them suspended. Save it for the pressure washer pump. It also does not come as a multi weight,any of those will be a detergent type.
Any 15-40 will be just fine as long as it is the correct weight and meets the specified API service classification. The OEM's make big money rebranding oil as you have discovered.
TLLOYD
Explorer
Nov 08, 2014
Interesting, when I asked the guy at Camping World what was so special about Onan oil, he told me it was non-detergent.

I was going to go with Rotella 15W-40.
WyoTraveler
Explorer
Nov 08, 2014
I use 15w-40 delo in my generator
enblethen
Nomad
Nov 08, 2014
Some Onan oil is SAE 10W40.
Some is straight 30 weight.
Any good quality oil will work. I use Castrol 15W40
I do dot see why you Rotella should work.
TEXAS
Explorer
Nov 08, 2014
The Onan oil cost 15.00 a quart. Because you are paying for the name. Any good quality oil will work. If I remember correctly. Onan oil is made by Valvoline.
bgum
Explorer
Nov 08, 2014
Any good quality oil that meet the specs is ok. The only thing special about Onan oil is the price.
RV_CONUS
Explorer
Nov 08, 2014
AND, all those Onan oil rigs.

I went to straight 30wt after reviewing the Onan site for oil/temps, as we are always in hot country, not hot as in CMA, but geographically hot!
down_home
Explorer II
Nov 08, 2014
I bought some Onan oil early on. After reading label, didn't need to pay that price.
I have went through a couple of diesel oils but now use Delo in engine and Onan diesel. It has more zinc wear additive like old engine oils have.
I fibbd by mis remembering. I put Royal Purple diesel 15w40 in the Onan.
MEXICOWANDERER
Explorer
Nov 08, 2014
A note: LPG engines -demand- low-ash oil. Aircraft engine oil is low-ash. When Shell Oil Co introduced it's Fire & Ice 20W-50 oil in 1971 I walked up to the quart-canner and I could smell the zinc dithiophosphate additive that made the oil able to sustain high temperatures. Rotella oil is huge tank blended oil. Rotella T is batch oil formulated in 3,000 gallon kettles. The specs standards for T were much stricter.