Originally Posted by Mad_Hatter
Originally Posted by Gokhan
There is no difference whatsoever between API Group II and Group III
in terms of how they are produced (refined, hydroprocessed, hydrocracked, etc.). The same plants and machines are used to produce both.
I don't believe I said there was. The only thing I believe I was addressing was the choice of terms "highly refined" in reference to grp3's. While I regularly read articles where the term "highly refined" or "more refined" is used w/respect to grp3's, in retrospect I thought a
better, more accurate term would be "severely treated" owing to the severity of the application of temperatures/pressures that yields a higher quality, grp3, base oil. So yes..same equipment, same process. No argument out of me there.
I'm not gonna touch the "what is a synthetic?" topic, mainly because you nor I are going to change our position so it's a waste of time to debate it.
Yes, the correct terminology would be "severely" hydroprocessed, but the word severely is not always used. Moreover, we still have the legitimate question of how severe.
Group II+ base stocks have VI = 115 - 119. Group III+ base stocks have VI ⥠130. GTL base stocks have VI ~ 135 - 145. VI is proportional to the inverse of Noack × CCS.
Chevron Group II and Group II+ base stocks (PDF)
SK Lubricants Yubase Group III and Group III+ base stocks
I don't even know your position on the issue.
My position is that the use of word synthetic is somewhat arbitrary, and if they don't tell me the viscosity index (VI) of the base oil, the only thing it means is whether it's 119 and below or 120 and above, which is a very rough description.
This is the formulators'/blenders' take on the issue:
They don't care whether it's Group II/II+/III/III+/GTL/PAO. The only thing they care is if the base oil can meet the Noack for a given xW range and industry/OEM spec. For example it's hard to formulate a 0W-20 with 15% Noack without at least some Group III, as the Noack for the 4 cSt Group II+ base stock is 16%.
The million-dollar question is whether synthetic oils perform better than conventional oils (such as capable of longer OCIs) of the same industry/OEM spec. AAA did that study, and the answer was that there is a trend that they do, but this is not always the case with every oil.
AAA spills the truth on oil changes
My take: The word synthetic doesn't mean much to me unless I know that the the VI of the base oil is above 125 - 130, not just barely clearing 120. You know that Pennzoil Platinum is a top synthetic because it uses GTL. Likewise Mobil 1 uses at least some GTL and/or PAO in most of their synthetics according to the MSDSs. Valvoline Advanced Synthetic seems to use Group III+ according to its low Noack and low VII content. In those case you know you're getting a good oil for your buck. Castrol Edge ILSAC (US) oils are more
promiscuous with their base oils than their competitors, and while sometimes you may get a high-grade synthetic, at some other times you may be getting a low-grade synthetic with a base-oil VI just above 120, which borders a conventional Group II+; therefore, check the Noack and CCS data if available to make sure.