“I understand the 10w30 will shear down -- but doesn't the engine manufacturer know this when they write the oil spec?”
Jason, I wouldn’t count on it. In a couple of the more extensive oil threads in this subsection, I go into the
minor differences between current Group II+ (‘conventional) and Group III (‘synthetic’) oils. However, in B&S’s recommendations, they treat these two as if they were completely different animals.
A decade or more ago, when the difference between ‘synthetic’ and ‘conventional’ was the difference between a Group I oil and a Group IV base oil, I think the manufacturers’ specs were appropriate. But now, they seem terribly out-of-date and even smack of plain old ignorance. And what about the synthetic blends? Many manufacturers don’t even address them.
What about Royal Purple 10w30 (synthetic) which shears down quickly? I’d rather have Schaeffer 10w30 Micron Moly (mineral oil) for an air-cooled engine because I’d bet almost anything that it will stay in grade longer. Actually
most PCMOs have had their barrier anti-wear additive amounts slashed and seem prone (or even designed) to shear down before the 2,000 or 3,000 mile mark for national average fuel economy reasons.
Part of me realizes it would be hard for the manufacturers to keep up with oil formulations which have been changing every handful of years, lately. That’s why their recommendations are the way they are: generic and out of date
Of course, most manufacturers will be happy to sell you their own brand of oil … but you know it’s outrageously priced and not nearly worth it. Probably merely an older formulation with extra ZDDP.
As
tmorris1 says above, most of these engines do really well on just about any kind of oil ... even if it isn’t changed often enough. So, is it really worth the manufacturers’ time to thoroughly research oils? Make sure customers get at least a dozen years of solid use from their motors? Probably not.
I don’t use straight-weight oils for anything anymore. For high-stressed air-cooled engines, 15w40 is a little easier flowing at start-up, has a killer additive package, the extra weight probably offers a bit more protection in these older design engines and if it shears down a touch, you’re still solidly in 30 weight territory.
I have single and twin cylinder, air and liquid-cooled power equipment engines and all of them seem to love the 15w40 oils (mostly Schaeffer’s synthetic blend) that I feed them.
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Bror Jace
