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TLLOYD's avatar
TLLOYD
Explorer
Nov 08, 2014

Whats so special about Onan generator oil

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
  • rivercity22's avatar
    rivercity22
    Explorer
    Apr 11, 2015
    Interesting reading as I am trying to decide what oil to put in my 2012 year Onan/Cummins gas generator. I have Rotella 15/40 in my garage but didn't think a diesel oil would be good for a gas engine, I couldn't find straight 30 weight in synthetic so I bought regular 30 weight. So it's either regular 30 weight, Rotella 15/40 or synthetic 10/30. What to do, what to do? The manual says to use the 15/40 or 30 weight for the temp range in my area but never mentions using synthetic. My gut feeling is go with the 10/30 synthetic and call it good.
  • MEXICOWANDERER's avatar
    MEXICOWANDERER
    Explorer
    Apr 11, 2015
    Aeroshell has a spectacularly low ppm residual ash content. Pretty much 0.0% sulfur content. The "T" grade of Rotella is small batch (kettle) oil and is made with superior base stock and precisely measured additives. It is better oil than plain Rotella. I learned a lot when I worked in Shell's "Compound House"

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