I'd like to know how much that Kawie oil costs ... and how long the warranty is for.
Often, the manufacturers want you to buy a $50+ extended warranty ... and getting owners to purchase vastly over-priced OEM oils may be a sneaky way to accomplish the same sort of thing.
As for 15w40, I use Schaeffer synthetic blend which flows pretty well in the cold. My second choice would be the newest formulation of Chevron Delo400 in 15w40. I used to recommend Pennzoil Long Life but they dumped moly out of their formula ... but may have added it back in since then.
I think the 15w40s are pretty stable and probably don't thin out much even when pressed hard in moderate-to-high temps.
If I felt any of my OPE struggling on 15w40, I'd use Schaeffer 10w30. Let's see
that stuff shear down.
I'd also bet the 10w30 versions of Delo400 and Pennzoil Long Life would be very shear stable ... but they are so rare.
Yeah, I think Amsoil, Mobil 1, etc ... will protect and offer a bit more net horsepower, but I haven't felt that 15w40 has let me down and hate dumping the synthetic aftre just 1 year of use.
In any event, I have never,
ever worn out an engine on a piece of OPE yet. Our snowblower is about 20 years old and I'd bet something else will break catastrophically before the engine detonates or wears out.
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Bror Jace