Silber Igel, we were having a similar discussion in this current thread … except that the subject is 15w40 instead of 5W-40:
https://bobistheoilguy.com/forums/threads/anyone-using-15w-40-hdeo-in-their-lawnmowers.134364/
But most of the principles are the same.
I would sum my argument
for the use of 5/15W-40 HDEP motor oils simply as follows:
1) The weight is a good choice for OPE that typically run high oil temps. They are a 40 weight at operating temp (which is a bit higher than the 30 weight recommended by manufacturers - B&S, Kohler, etc …) but these engines are quicker to shear and/or dilute their oil and I would say that during an interval of 30-50+ hours, they will be closer to ideal viscosity than a straight 30 weight which will become diluted and a XW-30 which will be diluted and sheared down, perhaps dangerously so.
2) The oil blenders update their oil formulations about ever 6-12 months. But B&S recommendations are usually updated only every decade or so. When they first began recommending multi-viscosity oils, they treated synthetics and conventional as though they were worlds apart in terms of performance. That might have been true in the 90s but in this age of Group II+ ‘conventional’ and Group III ‘synthetics’ that are very shear-prone, even in mundane, liquid-cooled applications. Again, their recommendations are at least a decade behind the times.
3) The last B&S manual I read (a “Quantum” engine on Dad’s wood splitter, I believe) actually said the use of straight 30 weight oils (the same they recommended for decades) could
damage the engine in sub-freezing temps. If so, why did they recommend it for so long? Why didn’t they figure this was a potential problem, say … in the late 80s? Again, they are way, way out of date with their recommendations.
4) The recommendation of a straight 30 or a multi-vis XW-30 seems to be driven heavily by availability. If you have to come up with a one-size-fits-all solution, this is probably an acceptable one … but that doesn’t make it ideal. If you are willing to put some thought into it and shop around, you can do better.
5) In a well-maintained, internal combustion engine, most wear occurs at start-up and a 5/15W-40 flows better at start-up and should contribute to lower wear at this critical run time.
You seem perfectly happy with a straight 30 weight because you live in a very warm area. In at least half of North America, straight weight oils are poor choices for year-round operation … even in spring or fall. If you start work in the morning, at or below the freezing point.
Other notes:
”The B&S HD30 from Home Depot is an excellent choice.”
I disagree strongly. OEM branded oils are usually of a decent, but not outstanding quality … but are highly priced … sometimes outrageously so. Convert the bottle price into a price-per-ounce then compare to some of the best oils (conventional and synthetic) that can be obtained on-line or in big-box retailers (Wal-Mart, Auto-Zone, Tractor & Supply, etc …). If one insists on a straight 30 weight, most HDEO blenders offer that weight as well. Any of those are likely to be superior to B&S 30 weight in terms of base oil quality as well as additive package.
Think of a B&S branded oil filter. Does anyone seriously believe these $10, tennis-ball sized filters are an excellent choice for the engines they fit? Or are you better off with a Wix, Purolator, Hastings, Baldwin, etc … which provide as-good-or-better quality for one-half the price or less.
Oil filters are not oil … but I believe the same principle is at work here.