Originally Posted by bluesubie
Further to what has already been said, and also provided by OVERKILL, Gohkan posted a good Lubes 'N' Greases article in the Interesting Articles forum.
The synthetics are coming
Quote
A "good portion" of the market also complies with General Motors' Dexos1 specification, which requires 13 percent volatility or lower. It's possible to formulate an SAE 0W-20 API SP oil with standard API Group III base oil, but to make a Dexos-approved product, the formulation must include "Group III+ in significant amounts, or even some Group IV," he said.
Dexos1 Gen 3, which is expected to make its debut soon, will clamp down volatility even further to 12.5 percent, according to Khaled Zreik, GM's powertrain & vehicle fluids technical specialist, who also spoke at the conference.
"The shift from Dexos1 Gen 2 to Gen 3 will increase the concentration of either Group III+ or PAO—it has to," Castanien said. "The only way to get that Noack down is to put in something less volatile, and I expect we'll see a shift to Group III+."
So generally better base stocks (0W-20) vs. usually lower volatility and less viscosity modifiers (5W-20). And now for the $60,000 question. Does it matter? In some applications and/or conditions,
maybe it does (thinking of myself since I'm running 0W-20 in a turbocharged Subaru)?
The reason why I decided to try out synthetic 5w20 in the first place was because the SN Plus versions of Valvoline Synthetic 5w20 have the lowest NOACK ratings for a 20 weight oil next to Ravenol. Not only that but according to the work Gokhan did on VII content, Valvoline was the best brand across the board with its synthetic 5w20 oils leading the way.
So maybe it is just that Valvoline has figured out how to make an incredibly solid synthetic 5w20?
To me it seems like if 0w20 is recommended for an engine it has much to do with the general composition and contents associated with 0w20 oil more than how similar it may look on paper versus a 5w20 even if the 5w20 may be considered better in some ways.