This is for my 92 Subaru legacy 2.2L 16 valve non turbo with 100K miles, Currently I'm doing an ARX treatment with 10w30 chevron oil.. what oil should I use after the treatment. On the cars manual it says 5w30 is not recomended for sustained high speed use and above 32 deg weather. Its recomending a 10w30 and 10w40 oil and also it says if the car is driven in high desert temp or used for heavy duty applications these oils may be used 30,40,10w50,20w40,20w50 .thanks for any help.