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Old 11-13-2011, 04:14 PM   #1
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Thought I had it figured out

After much help from the forum and an Onan tech, I thought I would visit my neighborhood WalMart, pickup 2 qts of 15W40 Synthetic Blend oil and be able to change the oil in my Onan 7000 gas generator. However, the only 15W40 available is Rottela which some have said is OK for a gas generator and some have not. On the Rottela container the API class is noted 'C' which I believe is for a diesel and another notation, SM. Does the SM notation mean it is OK for use in a gas generator? The Onan tech said to use 15W40 synthetic blend but so far I haven't been able to find an auto parts store that carries 15W40 synthetic or a blend.

I think the Rottela will be OK but I don't want to damage the generator.


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Old 11-13-2011, 04:28 PM   #2
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rotella in the blue bottle is the synthetic... its 5/40 weight. Really good stuff. the 15w is a lil cheaper but I like the 5w and use it in ALL my vehicles/power equipment. It exceeds all manufacturers recommendations too.
Kinda expensive by the quart... I buy the gallon jugs for $21

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Old 11-13-2011, 04:29 PM   #3
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Not to confuse you futher but you coul mix 15w-40 Rotella and synthetic 5W-40 Rotella.
I've never heard of a syn blend 15W-40. Motorcraft might have one.

And I can't think of anything in a diesel oil that will do harm to a gasolline engine.
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Old 11-13-2011, 06:00 PM   #4
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If you are having second thoughts, why not stick with Onan parts?

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Old 11-13-2011, 06:12 PM   #5
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I ain't paying $21/gal. I use Rotella in almost everything. Lawn mower, 57 Chevy & T'Bird.Power washer. 5 Gal 15-40w in 2- 2 1/2 gal jugs at Sam's for $63.
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Old 11-13-2011, 06:13 PM   #6
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Onan oil is Vavoline.
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Old 11-14-2011, 12:39 AM   #7
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Rotella-T and other diesel oils have more ZDDP than regular oil. It is an additive that prevents wear in high compression engines. I use it in almost everything too.
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Old 11-14-2011, 07:58 AM   #8
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lots of folks run the 15w40 rotella-t in their gennys. no worries.
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Old 11-14-2011, 08:08 AM   #9
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Originally Posted by W4MBG View Post
lots of folks run the 15w40 rotella-t in their gennys. no worries.
That is what is in ours. It is diesel though so it makes sense.
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Old 11-14-2011, 09:22 AM   #10
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Bottom line -- yes, the SM designation makes it OK. The language from the Onan manual that I quoted in your previous post said that (if I recall correctly) SJ, SH, or SG oils were suitable. Since they progress down the alphabet, SM would be even better.
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Old 11-14-2011, 10:03 AM   #11
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I would not hesitate to use Rotella in very nearly any Engine. it is one of the very best oils on the market and exceeds nearly every manufacturer's requirement on earth.

(What do I mean by nearly... i mean I've never seen one it did not meet or exceed, but I admit that I've not seen the requirements of EVERY engine on earth)
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Old 11-14-2011, 10:17 AM   #12
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The ZZDP is for flat tappet cams. Most new vehicles have roller tappets, that's why they took it out of regular oil. Rotella has it all.
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Old 11-14-2011, 07:54 PM   #13
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15w-40 also has higher detergent levels to deal with the soot that diesels generate, IIRC my Onan 5500 manual states 15w-40 is the preferred oil weight to use in most conditions...perfectly fine for your gas genny
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Old 11-16-2011, 01:13 PM   #14
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You can use Rotella. It used to have a higher ZDDP content, but it has recently been re-formulated. The reason oils for gas engines didn't have the ZDDP was Zinc causes early failure of catalytic converters, so the car manufacturers lobbied to have it removed from oil sold for automotive applications.

Not sure why the took it out of the diesel oils, but they have.

I used to run it in my 1969 Mercury 410, but now I have to buy an additive.

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