Sadly, most of the oil recommendations we read on these forums are anecdotal in nature; that is, they are based on small amounts of data that are not statistically significant, nor are they based on controlled tests comparing one product with another. That sort of information is very difficult for the consumer to obtain. Controlled comparative tests are run by oil companies, vehicle and engine manufacturers, and a few petroleum additive companies using standardized test protocols, but the results are not generally published, except to say that an oil passed the minimum test requirements. Consumer Reports last ran an oil performance test a few years ago, carefully measuring engine wear. I don't recall whether they compared mineral oils vs. synthetics, but they did show that there was no difference in engine wear between changing engine oil at 3,000 miles and at 12,000 miles.
Based on published reports I considered reliable, I starting using synthetic oils about 7 years ago, in all of my new engines and vehicles, including small engines. I use conventional oils in my older engines with higher wear and leaks. For synthetics, I'm using Mobil 1 in some engines, and Castrol Syntec in others.
Other products that I believe work well ( although my data is here again anecdotal) are Chevron Techron fuel system cleaner, Marvel Mystery Oil as a top cylinder oil, Rislone oil additive for noisy hydraulic valve lifters, and any one of several automatic transmission "miracle worker" additives, which seem to actually have worked in perhaps three or four cases to free up stuck valve bodies.
I'm considering starting to use a gasoline preservative additive for stored gas. Sta-bil claims to have 70 endorsements, but looking online I don't see detailed statements from any company I recognize or trust, and I used to work in the petroleum additives industry, selling directly to the oil refineries. However, Briggs and Stratton has their own brand of stablizer, and I do trust them to have done their homework. The oil companies call most aftermarket additives " mouse milks" , and will tell you that most of them probably won't hurt your engine, but they will certainly empty your wallet. And as for any oil brand that won't submit to standard API or ASTM testing procedures, they're hiding something. Probably that " something" is that their oils sell for a premium, but the performance is the same as less expensive oils.
