Onan Generator oil

[Engle]

I was calling around looking for Onamax oil for me 7K Onan generator.

One place said they always use 10W30. any brand.

I called the RV shop that did my service last year and he said 5W30. any brand

The manual says use Onamax 15W40 but I cant find it locally. Will a name brand 15W40 motor oil work just as good? All of the 15W40 that I find says for diesel engines.

Can it be regular oil or does it need to be synthetic? I will change it every year or 150 hours, whichever comes first. I doubt if the original owner used synthetic, even if he did own a Jiffy Lube. He never used synthetic in the engine.

I have heard so many opinions, I don't know what to believe.

Thanks, Leo

[JC2]

Originally Posted by Engle

I was calling around looking for Onamax oil for me 7K Onan generator.

One place said they always use 10W30. any brand.

I called the RV shop that did my service last year and he said 5W30. any brand

The manual says use Onamax 15W40 but I cant find it locally. Will a name brand 15W40 motor oil work just as good? All of the 15W40 that I find says for diesel engines.

Can it be regular oil or does it need to be synthetic? I will change it every year or 150 hours, whichever comes first. I doubt if the original owner used synthetic, even if he did own a Jiffy Lube. He never used synthetic in the engine.

I have heard so many opinions, I don't know what to believe.

Thanks, Leo

Shell Rotella 15w-40 dino oil is what we have always used in our gennies. Changing it every year or 150 hrs, whichever comes first, makes synthetic oil unnecessary as a "good" quality dino oil will be more than adequate.

[BFlinn181]

Onamax is available at most RV stores, Camping World, Tweetys, RV Parts Factory, etc. Also probably available at any Cummins shop.

[paz]

Originally Posted by Engle

I was calling around looking for Onamax oil for me 7K Onan generator.

One place said they always use 10W30. any brand.

I called the RV shop that did my service last year and he said 5W30. any brand

The manual says use Onamax 15W40 but I cant find it locally. Will a name brand 15W40 motor oil work just as good? All of the 15W40 that I find says for diesel engines.

Can it be regular oil or does it need to be synthetic? I will change it every year or 150 hours, whichever comes first. I doubt if the original owner used synthetic, even if he did own a Jiffy Lube. He never used synthetic in the engine.

I have heard so many opinions, I don't know what to believe.

Thanks, Leo

If you read all the fine print on the label, you will find most 15W-40 oil will also work fine in gas engines.

The designations like CJ-4, CI-4, etc. are the diesel specs. The "C" in the designation stands for Commercial. Look for designations like SL, SM, SJ on the label. Those are the specs for gasoline engines. Make sure the oil has the same or later spec than specified in your generator owners manual. See American Petroleum Insitiute Engine Oil Guide.

I used Mobil Delvac for my last Onan oil change (gas). It says it works for gasoline engines, and the label is marked with "SM, SL."

[soneil422]

I use Shell or Valvoline 15w40 Diesel oil. My generator states that 15w40 is good to use in temperatures between 10-100. The thinner 5w30 oil would work if you are camping in colder temps. I don't camp in the winter and don't need the thinner oil. Protection to 100 degrees is more important to me!.

I also spoke to a small engine repair shop and learned that small engines (generators and lawn mowers) have square cut tappets, like numerous diesel truck engines, instead of oval like a cars push rods. The diesel truck oil has a special additive that adheres to the square tappets and provides more protection than standard auto oil.

So it's always a 15w40 for me. Brand is not important as they are all good oils.

[soneil422]

And I can get a gallon of Shell Rotella Triple T (dino) at Wal-Mart for $12.99 a gallon. Good for two oil changes and a whole lot cheaper than Onan oil!

[Engle]

Thanks everyone..... I called Shell oil help line this morning. They said it is ok in any gas engine that does not have a catalytic converter. Something about an additive in the oil reacts with the converter. He said it is OK in old cars but not OK in new cars. It all depends on the exhaust system.

[LeeRevell]

Nice to know about Rotella T - a lot of us KLR650 motorcycle guys use it. I have nearly 45,000 miles on her, and it still runs like a Timex. Have never had the carb off or the cases split.
I'll try it in my portable gensets.

[Virago-Rider]

Originally Posted by LeeRevell

Nice to know about Rotella T - a lot of us KLR650 motorcycle guys use it. I have nearly 45,000 miles on her, and it still runs like a Timex. Have never had the carb off or the cases split.
I'll try it in my portable gensets.

I use Rotella in my 1985 Yamaha Virago XV700. 138,000+ miles still running great, 47 mpg.

[Ray,IN]

Most recommend using the same oil you use in the chassis engine.