Why would a good synthetic or even conventional oil without a mower manufacturer label not be suitable for constant speeds? People do it every day on the interstate highways. I've run my motorcycles for many hours per day at about the same RPMs as my mower runs for one hour per week.
I'm not trying to argue but simply have never seen evidence to support the notion that a brand-specific oil (e.g., Kawi) is superior to something else (e.g., Mobil1) in a Kawi engine. After 20 years of seeing these claims on motorcycle and other forums I've never seen one iota of evidence to support them. A good way to prove your point would be to send a sample of fresh Kawi oil to Blackstone Labs and ask them if there are any differences compared to an equivalent mainstream oil of the same viscosity and type. Kawi KTech 10w40 oil, for example, is API rated SL, just like most every oil you can pick off the shelf today. That means it must meet specs for compatibility with clean running and friendliness to catalytic converters, which a mower doesn't even have. If Kawi oil was special it would likely not have a contemporary API classification and would have extra ZDDP added for protection during fatal mishaps, like no oil pressure.
Also, I notice my manuals don't even mention Kawi oil, even as a recommendation. All this is not to say that Kawi oil is inferior in any way, but simply that it is likely conventional oil with a very high price tag.
You are correct in your assumption that BRAND specific oil is no better than any other USE SPECIFIC oil, provided both are within specifications.
It is the same with oil filters, I use the same specification filters from the same factory as the factory branded ones and there is no difference between them either apart from the price .
I do the same with blades all OEM after market parts , except that some of these are in fact better than the ones the makers fit.
Back to oils, no mower company makes oil all they do is buy it in with bottles that have their name on it then distribute it through their parts network, which by lower volumes means higher prices than the same oil bought in a different bottle from a high volume sales outlet.
When it comes to what is in the bottle there is a big difference.
As previously mentioned, no oil is going to make your engine blow up.
Cheaper oils will allow for increased wear rates and perhaps more oil useage.
All oils start life as a crude.
The oil refineries analyse the oil then work out what they can make out of it most economically.
Australian crudes are not economic to turn into petrol but they make excellent lubrication oils.
The oil gets split down according to its molecular weight ( not the viscosity wt you see on the bottles ) then a particular fraction will get blended to make a particular type or end purpose oil.
Car oils and mower oils are generally made from a different oil base and that makes them fundamentially different.
Specialist oil BLENDERS buy unblended base oils from the refineries and build them up with their own addative package.
The small specialist oil BLENDERS can afford to use a better package than mass oils because they service the section of the market that is not as price sensitive .
So there are 2 basic things that determine the suitability of an oil for a particular use, the base oil & the package.
No oil company will tell the customers either of these and the packages are bit like KFC's spice recipie , a very close guarded secret.
The heavier the oil the more it costs
So I can make a 30wt oil from a 30 wt base , a 20wt base a 10wt base or even a 5wt base.
As the wt of the base oil gets lower, it get cheaper and the oils overall performance becomes more dependent upon the addative package which has a finite service life, a finite shelf life & a finite temperature range.
SAE 30 ower oils are all formulated from a 30wt base so they will perform as a 30wt oil even after the package has been either consumed , reacted , oxadised or burned out.
Some easy to understand differences.
Modern auto oils have to allow the car to start on the first cylinder that dose a full cycle so they have to be made from thin & slippery when cold oils to reduce the drag on the starter motor which allows the engine to spin faster at start up so it can fire on the first pot that went through a full induction cycle.
Mowers do not need to be able to do this ( yet ) so can be blended from a heavier oil.
The heavier the base oil the longer it will last so even after the addative package has been consumed, the oil will still work & not totally break down .
One of the big reasons why Honda push mowers start so easy is they use a 10w base oil which has less viscious drag at room temperature than the plain SAE 30 that B & S recommend.
In defence of Scott, his synthetic oil will have a lot less drag than the Honda 10w so any engine using that will be even easier to crank.
I have a lot of old frail customers and they are amazed when I service their mowers & they can suddenly start it , the biggest difference is the fact I use 10w40 in their engines.
The caveat to this is the 10w40 will not last as long as the strait 30 so will need more regular changes to maintain full protection and will leak more.
To fully understand exactly how the oils work & what the chemistry actually dose requires at least a graduate level in organic chemistry which is why there is so much confusion.
Most people can not comprehend how their washing up detergent actually works let alone a very complex fluid like oil.
To make things easier the industry use codes for BASIC performance levels &/or addative packages and these get printed on the bottle, Sf, Sl etc .
Where people get confused is a higher rating is not necessarily better for your end use than a lower package. It is a case of using the RIGHT package.
An old Ford flat bed & a Ferrari are both vehicles. both can tow trailers . The Ferrari is a better vehicle than the Ford , but the ford will tow your mower trailer a lot better than the Ferrari will.
OTOH if you are driving coast to coast on an interstate the Ferrari would do that a lot better, but go on unsealed back roads & you will be better off back in the Ford.
And finally, the actual service life of an oil will depend upon the oil you start with, the condition of the engine it is used in, the way that engine gets used, the fuel that the engine uses and the enviroment that it runs in.
Way too many variables for a one size fits all solution.
