I think i'm going to switch to a euro spec oil. Per the manual it just needs to have a SN, SM or ILSAC approval rating. Like I mentioned the Castrol C3 oil is the leading candidate and it has a SN rating. Amsoil XL is also a little better than Amsoil signature and has ALL the ratings.That’s unfortunate but it’s expected. I guess you can keep doing the UOA monitoring the oil dilution condition like Silly Wabbit suggested, in the mean time try a different oil. I’d try newer SP / GF-6 oil next time such as Idemitsu SP/GF-6 5W-30 oil. And here is ILSAC GF-6 performance relative to GF-5 and API SN Plus performance:
View attachment 297015
And Idemitsu SP/GF-6 5W-30 oil claims the following improvements over GF-6 standard although many say they’re exaggerating:
- 30% more protection against engine wear
- 26-46% reduction in oil consumption for longer life
- Up to 24% improved fuel economy
- 90% more resistant to viscosity increases
- Three to four times more protection against cold startups
- 91% reduction in low-speed pre-ignition (LSPI)
- 6% cleaner engine
In case anyone looks at this with the same problem for the grade of oil specified (in this case 5W-30) you want an oil with a higher viscosity at 100 C and a high HT/HS value. This will resist dilution better. The Idemitsu GF-6 would actually be a downgrade from the Amsoil Signature as it has lower values for both of those.