I finally upgraded to a "Larger Generator" As the 4000watt was feeding all my 110 but was pushing it.
I have in the past run the old 1993 8HP Cast Iron Sleeve Briggs for 7 days with oil changes every 20-25 hours of run time that I bought new.
Since Briggs and Stratton is no longer what they were I have changed over to Honda when I buy any new small engine equipment.

I posted above due tp the fact that when used it will be used in the south and in heat and may end up getting used hard
Plan is to run it as a brake in and swap oil.
The tech says the GX390 13HP takes 10-30 Dino but you can use 5-40 In Dino or Mobil One.And that the most important thing is what I am doing. To run half a tank to full tank of gas as brake in and do the oil change. That most just make sure that it rind and pick it up. He must have had time on his hands as I just wanted to know if they had recomendation on oil grade of other than what it was shipped with.
I did look at Bobistheoil guy and some said they used 10-30 and 5-40 but no one said they used 10-40. So assuming that in the 10-40 the 10 is to thick for tight clearances. And that they saw some gens fail in Florida after Hurracanes with use of the 10-30 in extened run times in hot summer southen heat.

Thoughts

Maybe 0-40 mobil one.

"I have in the past run the old 1993 8HP Cast Iron Sleeve Briggs for 7 days with oil changes every 20-25 hours of run time"

OMG, seriously? You change oil every 2 days?


I have an 11hp honda in a pressure washer that gets probably 500 hrs a year use. It gets USED. Sidewalks, carpet, the siding on the house, the roof, parts, commercial mower, swimming pool, deck, bbq, compact track loader, 18-wheeler and my vehicles are proof: no rust.

I think I've changed oil in it 3 times in the last 17, 18 years? What do I put in it? Pfff, whatever is laying around, 15-40 diesel-spec.

Still starts on the first pull with the choke on.

Oil changes are over-rated: up to 10,000 mile intervals is not un-common. And, NO, it's not "cheap insurance", I have yet to have anything mechanical let me down because the oil was "old" or "houred out". It's a waste of money if you fuss around changing oil because you seen a pennzoil commercial on tv

Page 9 of the factory service manual for the engine tells you what type of oil to use?
https://cdn.powerequipment.honda.com/engines/pdf/manuals/31ZH9600.pdf

Wouldn't 10w30 and 10w40 be the same thickness at the 10 end of it?

YES the 10W part is the same viscosity.

i just use the same synthetic oil in my mower and snow blower that i use in my car and truck, 10W 30. i bought both used with the crappy B&S motors. both have run flawless for the last 15 years. change the oil when it looks dirty, about every 3-4 years.

The tech called back as i left a message.
He said cold was 10w30. And warm was 5w40 but no 10w40.
And they recommend a,brake-in of 3 or 4 Gallons gas minium and oil swap as things may be in the oil. Kinda like we do with old car motors we build.
They want a run time of 30 min every 30 days or 60 min every 90 days. To get oil hot to get moisture out ( if that is even possible)and charge the battery.
And oil changed every 3 days if used constantly unless Mobil-1 10w30 type is used.
Mobil-1 10w30 was 6 quarts $10.00 off at Sam's Club delivered to.my door so $27 and change.
Will use the Honda Dino it ships,with to brake in for a half tank to full tank of gas as it may have brake in additives in it.
And put the Mobile-1.
He said keep a lot and receipts as it has 3 years and 3 more I bought so 6 years of coverage.
That Honda denies all claims with the oil excuse.
Seems like it may be over kill on my part. But oil is cheap.
The old 8hp B&S may have had to many changes but is still going.
On close out Napa 30w that was cheap.
The wife's Snapper Mower get the oil and filter as recommended as,well as the edger and compressor.

The Honda manual is not the same as the one supplied with the generator.
Strange. Maybe it has ti do with use?

I would run it hard and dump the oil and take the oil temp with a thermometer, as long as it is 260 degrees or lower anything will work. If it is at 260 or close use synthetic for sure. I would find it hard to believe the honda would supply a motor that had insufficient cooling, but there is only one way to know for sure. I use whatever oil I have in small engine's, 15-40 conventional or 0-40 synthetic for the most part, and have never had problems.