15/40 oil for propane generator

daugen · Oct 7, 2019

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 · Oct 7, 2019

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 · Oct 7, 2019

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 · Oct 7, 2019

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 · Oct 7, 2019

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 · Oct 21, 2019

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 · Oct 21, 2019

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 · Oct 22, 2019

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 · Oct 22, 2019

Rebeldad1 said:
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 · Oct 23, 2019

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?

RalphVa · Oct 23, 2019

I use 5w30 M1 in my lawn mower engines. Should be fine for your Onan air cooled. Think the only difference between diesel and gasoline engine oils is extra detergent to keep the soot in suspension on diesel oils. Diesel oils can be used in gasoline engines, if the 15/40 is what is speced and still under warranty, just use what you use in your tractors and then when off warranty, switch them all to 5w30. That's what VW had speced for use in its diesels for many years. Castrol 5w30 from VW is what I use in my JD and Isuzu diesel engines here in Va. Plan to switch to 0w30 M1 ESP when I'm out of the Castrol stuff because I'm an Exxon Mobil guy who worked in lube oil industry for 31 years and know that M1 was always the best. (Never saw any tests on the Group V stuff that's out there now. Bet it's just as good. Don't think it was there much when I was working, pre 1998.)

Ralph

Texasmark · Oct 23, 2019

I have been using Rot T6 5W-40 full syn in my ll kW Generac since new in 2014, and my two Bransons since new. No reason not to! The lower the first number the better low temp viscosity which helps to prevent "dry" startups....like my weekly 15 minute automatic cycling to keep things in working order. Most oil charts on newer equipment now list syn multigrades and the temps along with dino HD and regular single grade and their recommended temp ranges of operation. Mobil 1 0W-xyz states on the container that it meets or exceeds all mfgrs specks for 5 and 10w-30. What gets me is I have a lot of DR equip made up in Vermont,or sold from there. The maintenance package oil that they sell is labeled DR and is 30W HD. I can't believe in today's world they sell that viscosity especially in Northern climates.

nyone · Oct 23, 2019

Considering DR power equipment is in business with generac i would have to say they stste 30w oil because thats what the chinese wrote in the manual.

Texasmark · Nov 1, 2019

I run Mobil 1 0w-30 in my 11 kw Generac purchased new in Feb. 2014. Same oil that goes in my 2011 Silverado P/U. Exceeds owners manual recommendations.

Copperhead · Nov 9, 2019

On my Detroit 60, I use a Schaeffer syn blend 15w40 CK4 in the summer and Schaeffer syn blend 10w30 CK4 in the winter. Just changed oil. 1,038,811 miles and 22,496 hours on the engine. Still only uses about 1 qt per 11-12,000 miles. Engine all original except the water pump. Operates from 100F+ to -25F. While synthetics are great in niche applications, I am not convinced that they really are a value and offer any longer engine life for the average user. I also use Schaeffer 5w30 syn blend (gas version) in my pickup truck and SUV and other stuff including lawn mower, gator, generators, etc. I do use a Pennzoil conventional 10w30 in the wife's 2006 Cadillac CTS 3.6. Again, all original engine. Nothing wrong with a full synthetic, but given the quality of all base oils today, the luster of synthetic has grown a little dim. Except for special applications, not worth the money.

jgedmond · Nov 9, 2019

My Cummins / Onan whole house propane generator recommends 5W30 full synthetic.

Texasmark · Nov 9, 2019

nyone said:
Considering DR power equipment is in business with generac i would have to say they stste 30w oil because thats what the chinese wrote in the manual.

It was there back in 2005 at least, who knows how long before that, when I bought my 52" Pro Z lawn mower from them, first of numerous purchases and still the same oil in the kits.....back when they had BS engines made in the USA on their equipment.....last piece I bought was an updated leaf vac and the engine was of their own namesake and it looked like it was of Chinese origin......but the two engines I have from there are fine, well designed, built, owner friendly machines having amenities not available on most BS engines of the same size.....per the horses in my stable.

daugen · Nov 10, 2019

I have the same DR leaf vac, one with largest motor on it, definitely a top quality Chonda, and the black paint job on that engine looked about a quarter inch thick.
Still looks like new three years later, granted it's one of my lowest hour per year motors. Engine always starts immediately, but very noisy clattery muffler.
and I remember the requirement for straight 30W, which I had plenty of in the barn. Now running my normal 10W-30 full synthetic in it. My normal process has been change the oil at 5 to 10 hours, use conventional oil as spec'd back in it, and following year at oil change time switch to full synthetic or part synthetic. I use semi-syn in the tractors and full syn in just about everything else.

Perhaps the chemistry has changed, but for a long time they said full synthetic was too slippery to have rings set in properly or quickly. That may be all baloney now, even base oils are greatly improved as noted above. And more and more cars/trucks come with full synthetic as oem, which I 'm sure has most to do with fuel economy.

During warranty I toe the line, and therefore bought a couple of quarts of the Onan labeled 15/40 oil. Had to hunt around to find it at a reasonable price, still expensive, must be the fancy label...

The 3.6kw gen in my rv is a 3600 rpm buzzbomb. Worse it starts up and goes full speed immediately, no warm up period.
No oil filter either, this is basically a lawn mower engine, and that's the way I'll treat it.
Being propane fired, I don't expect the plug to foul or have carburetor issues, so should be reliable like my whole house gen.

appreciate all the comments and feedback. I simply had never seen 15/40 conventional oil with gas engine ratings.
Makes one wonder why Onan/Cummins goes to all the trouble of having someone custom blend it for them.
Part of this was my curiosity, what do they know I don't?...

Texasmark · Nov 30, 2019

nyone said:
Considering DR power equipment is in business with generac i would have to say they stste 30w oil because thats what the chinese wrote in the manual.

They had it in the manuals back in 2005, my first purchase. I think the Generac purchase was a couple of years ago when things really changed in the marketing department and products offered.

Rebeldad1 · Dec 7, 2019

fried1765 said:
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 ??

Maybe... maybe not. I went with AMSoil because it was the best that I could find. I serviced several hundred customer cars with AMSoil and felt very comfortable with the decision. It was the only synthetic oil at the time that listed a 100% guarantee that if a engine failed because of their oil they would replace it. Also the only synthetic oil where you could phone directly to the lab that makes the oil to ask questions. Big plus for me.