"my info sae30 is txt book, your 15w40 is opinion"
The manufacturers' recommendations are notoriously out of date. I had long rants about Briggs & Stratton on this board years ago regarding their foolish recommendation of synthetic 5w30 or mineral 10w30 ... as if there was a massive difference between the two ... when we know there is sometimes just a slight difference (if any). And after recommending SAE30 across the board for decades, they have
finally figured out that starting one of their engines using SAE30 in sub-freezing conditions can actually
damage the unit. Nice that you've joined the party guys ... at least a decade late.
You are correct. Kohler manual for the motor in a non-defined application in non-defined operating conditions says to use SAE30 ... but that is merely a generic guideline which can (easily) be improved upon.
My info was not merely opinion ... much of it having to do with pour points and add-packs is
fact that can be documented by comparing VOA lab tests.
flatlandtacoma, I was assuming a PCMO SAE30 above ... as the manual does not specifically say to use a HDEO SAE30, or does it?
As for pour points, I'll take all the help I can get. I've been out there on the frosty mornings trying to start an old wood splitter, tractor or snowblower with SAE30 in the crankcase. 15w40 is definitely an improvement ... but yes, in applications that you know will involve colder temps, and in engines that are not notoriously oil-burners, 10w30 may be a better choice. I didn't say it wasn't.
Back to SAE30 vs 15w40 HDEO, I'll still take the 15w40 on cool mornings as many people believe that most wear occurs at start-up and every bit of additional flowability is an advantage.
Good point on the fuel dilution. For people that religiously change their OPE's oil every 25 hours, there is not much of an advantage. However, for people that go longer (sometimes to the point of neglect) the 15w40 HDEO is added insurance and the superior choice.
Any evidence that a 15w40 makes any OPE run hotter? The theory is valid ... but totally unsupported as far as I know.