Originally Posted By: carman594
How does SSO compare to GC?
SSO is designed to meet API SM and ILSAC GF-4 specifications; GC meets API SL. This means SSO is formulated to be friendlier to sensitive emissions systems, whereas GC may have higher levels of certain anti-wear and cleaning additives (which may or may not be important to your particular car).
SSO is designed to meet ACEA A5, whereas GC meets ACEA A3. This means SSO has a lower HTHS viscosity, which means it is a bit thinner in severe conditions but may improve fuel economy as a result.
GC is explicitly approved by third parties, including vehicle manufacturers. SSO is designed to meet many third-party specs but isn't actually approved. That doesn't mean Amsoil is lying to you, but it may have implications if your vehicle is still under warranty.
This isn't an exhaustive list, mind you. It's just what I can tell from publicly verifiable info.