If a oil now has a dual rating of SN plus GF-5 does it make for a better oil ? If so why in your opinion ? I was prompted to ask due to new formulation of M1 0W30 oils now being advertised as being reformulated to meet SN plus GF-5 ratings ...
I don't know the answer, but there must be some differences between SN and GF-5. For example, in our RX, I run the Pennzoil HM 5W30. According to Pennzoil, all Pennzoil® motor oils, conventional or synthetic, will be reformulated to exceed the new ILSAC GF-5 / API SN specification (except Pennzoil High Mileage Vehicle, which will be API SN only).
"API SN, when licensed with Resource Conserving, is equivalent to ILSAC GF-5." But you can have API SN without RC:
"API SN with Resource Conserving is equivalent to ILSAC GF-5. In contrast,
API SN does NOT require
* Sequence VID Fuel Economy
* Sequence IIIGB Phosphorous Retention
* TEOST 33C
* Emulsion Retention"