I personally think it's hogwash.
From an air-cooled perspective: oil is oil is oil. The primary difference between conventional water-cooled IC engine vs air-cooled IC engine is that while former type runs in a thermally-controlled fashion (oil temp variation while engine @ operating temp is very small); air-cooled engine exhibits a larger variation of thermal conditions and that, in return, resulted in the higher rate of oil vapourisation during high load/high-heat/poor-cooling situations.
and yes, typical 10W30 will "boil" off at a higher rate than that of a monovisc SAE30. That being said however, even B&S (the biggest OPE maker in NA) now recommends the use of syn multivisc oil in the line of products:
http://www.briggsandstratton.com/support/frequently-asked-questions/Engine Oil Recommendations/
2 issues typically go along with the oil consumption RE: ope engine types:
(1) the lack of valve stem seals. This is rather common on flatheads and some versions of OHV..so oil will seep past the valve stem and guide and get burned in the combustion chamber (esp. when the clearances becomes bigger as the engine ages).
(2) thinner grade oil gets "boiled" off at a much higher rate than, say, monovisc SAE30. A more robust higher visc syn oil (like 10W30/10W40, 15W40, etc. or even 5W30 during winter time) would work wonders for these syn base oil resists "boil offs" better than those multi-vis conventional oils of yore.
I personally take your small engine shop's comment with a grain of salt, citing that:
A. I treat all OPE (be it my own or the ones that require my help fixing) the same: I use whatever I have on-hand (10W30/15W40, semi-syn, delo, HDEO, etc.) I do warn the owners that they must check their oil level everytime before they start they work (mow job) and top them up whenever possible.
B. Most of the OPE engine owners neglect their machines so badly, that oil is the least on of their worries (concerns). my 675 missed oil changes for 6 seasons in a row and does that tells you a story?
Lastly: i typically question many small local engine shops knowledge and integrity, citing that (a) many of them would lie through their teeth just to get by, either intentionally (like E10 was the cause of their engine issues (which 9out of10 was not); and (b) they lied about services performed and overcharged customers for jobs that they didn't perform.
Lastly: to me, Mobil-1 is just another syn oil by a national brand, and I treat it just like any other national brand of syn based motor oil (nothing special to me).
Q.
