15/40 oil for propane generator

[daugen]

Would appreciate some advice. My little Onan/Cummins propane gen in my new rv specs 15/40 oil.
Well that's easy right, 15/40 is everywhere. Sure is, but it says Diesel on every container I've researched, and I use Rotella T5 15/40 in my tractors.
Where I'm getting hung up is the SAE labeling, as all the 15/40 oil I'm finding has ratings for truck use, different lettering than passenger gas engines.
My gut tells me the diesel oil is overkill for the little lawn mower engine in this gen, but I also don't want to ruin any warranty I have. So for first oil change, I will use the oem oil, which is conventional btw. Onan must have someone formulate this for them, who is unknown. I went over every oil in Walmart yesterday and a local auto parts store and not one appropriately labeled oil except for the oem.

https://www.amazon.com/Cummins-3265...ywords=15w40+onamax+oil&qid=1570450436&sr=8-1

I want the highest heat rating since I intend to travel through the SouthWest. For that, Onan is clear on 15/40 use. They also say straight 30W is preferable if low temps are not encountered, but I can't depend upon that, plus it will make the engine harder to start in colder temps. And I'm not sure of anyone making straight 30W synthetic at normal pricing.

Is there any reason why I can't use T5 or T6 motor oil, or Delo, or..., to run in this 3600 rpm propane powered small engine?

Ten bucks a quart just annoys me, like I'm throwing away money to Onan marketing.
Thanks. Drew


Cummins Onan RV QG 3600 LP - 3.6KYFA-26120 - 3.6kW RV Generator LP

 

[Roadworthy]

Look for the API ratings on the container as well as the oil weight. There should also be API ratings on the official Onan container. Get something equivalent or better. If it is rated for diesel use that does not mean it's not suitable for use in regular engines, just that you can use it in a diesel, too.

 

[Storm56]

I have been using 15W40 Diesel Oil in small gas engines for about 30 years now. Have never had an issue. Only small gas engine I do not is a Kohler 25 HP on a sawmill. It calls for 10W30 suposedly because of the hydraulic lifters.

 

[daugen]

thanks guys, I mixed up SAE with API.
the challenge is when they only list the diesel rating and not the API gas letters. I don't know what letter we are up to now,
but I saw an N on synthetic today.

I do think it's interesting that Onan has 15/40 conventional oil packaged for them. I'm sure it's the one grade that
keeps the warranty claims down.

here's what manual says:
Use API (American Petroleum Institute) performance Class SJ, SH or SG engine oil, which may be
in combination with performance Class CH-4, CG-4 or CF-4 (for example: SJ/CH-4).

but what if they list none of the classes starting with S?...
For example, Rotella T5 shows none of the S class ratings on the jug, only CH4 to CK4

 

[RjCorazza]

I looked at a few 15w40 oils, and didn't find any with the SJ (minimum) API Classification. I use a 5w30 diesel oil in my gas vehicles, but it also carries an S rating (forget which).
Personally, I would use a 5w40 or 10w40 in with SJ or better rating rather than a strictly diesel rated 15w40. The lower W(inter) number simply means that the oil will thicken less in cold temperatures.

 

[Rebeldad1]

I use AMSoil 15/W40 marine. Works great in any of my 10W30 gas engines as well. Expensive? maybe but you cant buy better protection for your engines. Havnt replaced any engines yet

 

[daugen]

Rebel, that sounds like a very high spec oil, sure should work.

As I sit here plugged into campsite power and not running my gen at all.... unit isn't going to get many hours at all.
I do have a friend with a cabin in the Catskills where I would dry camp, but unlikely I'd run the a/c there and everything else is DC and propane.

I started using Mobil 1 at least twenty years ago, maybe longer. In practice, seemed to make starting a little easier.
But I've never replaced an engine either. Now I buy full synthetic but not as name brand conscious as I was before. Walmart and even Tractor Supply full synthetic oil has seemed to do very well in what little comparison testing I have read, or can find.

 

[nyone]

Lol you guys crack me up.."havent replaced and engine yet" lol. That dosnt mean anything.

There are many good oil test results out there for your viewing. Go check them out.

Project farm on youtube did a synthetic oil shoot out test recently. If I remember correcty mobile 1 and lucas did not to to well.

 

[fried1765]

I use AMSoil 15/W40 marine. Works great in any of my 10W30 gas engines as well. Expensive? maybe but you cant buy better protection for your engines. Havnt replaced any engines yet

I am 79 years old, and have used just about every type/brand oil known to man.
I too, have not replaced any engines yet.
Could I have done even better with Amsoil ??

 

[daugen]

There are many good oil test results out there for your viewing. Go check them out.

it would be helpful if you referenced them. Bob the Oil Guy?
And what particular specs would you find most important for a generator?