Originally Posted by Mad_Hatter
Then why don't formulators use grp2 base oils in EP lubes? Or do they use synthetics because they know the finished lube is gonna be used in less than perfect/ideal engines, so using a full syn affords them a measure of protection? (not trying to be argumentative, just genuinely curious)
They use the cheapest thing that will meet the minimum specs. That's a combination of external specs (ILSAC GF-5, for example) and internal specs (‘we want to label the product as synthetic so we can sell it at a higher margin,' for example). IOW, if the product you're looking at is anything more than a solvent refined grp I fluid, that's because it can't pass the necessary tests without those higher grade bases.
I'm not certain whether a purely grp II based engine oil can pass all certification sequence and lab tests for any current PCMO spec in a 0Wxx grade. I think not, but not certain. A 10w30 might be doable with grp II or mostly grp II.
Some here would know. We'll see whether they say.