Castrol oils are generally more shear stable and typically 'thickens' (as upwards of virgin cSt) in engine oil OCI's beyond say, 10k miles.
Yeah, well it almost "thickened up" out of grade.. although I'd be surprised if the engine couldn't do a SAE30.
Sure, shear thickening is a "thing" as well as thickening from soot but his Insolubles% is low and the fuel dilution and lower flash point seems to indicate, to me at least, a thinning of the oil should have occurred. But I suppose it's possible to have both thinning (fuel dilution) and thickening (soot/evaporative loss-noack%) effects happening concurrently?🤔🤔
Guess this is a first for me... seeing an oil do this after a 10k run, it's 100c kv is better than the starting 100c.