Originally Posted By: bbhero
Hate to disagree but Castrol GTX 5w20 just tested was 12.1 NOACK and Quaker State Conventional was 11.4. So these "conventional" oils actually surpass the Dexos specification for volatility. These were recently tested in the last year as well.
Hi BBHero, yes, no problems and always good to hear from you. I do recall some excellent conventional figures recently, but I couldn't quote the actual numbers off the top of my head. Most of the figures I got from google were a few years old (circa 2013) but, apples with apples, most of the figures (M1, GTX, Quaker State Conventional) were about the same age.
I, like you I believe, tend to follow the specs on the bottle, as these act as a guarantee of what quality you can expect inside. With Noack volatility API SN is 15% max, while Dexos1 and A5/B5 and A3/B4 are all 13%, with MB 229.5 being 10%.
This removes the confusion of asking yourself, "did I get the good brew?". For example Noack figures returned from PQIA for Pennzoil Conventional 5w20 gave 6.5% for a bottle purchased in 2013, and 13.1% for a bottle purchased in 2016. Same bottle, different contents.
So to answer the OP's original question a different way, as I can't test every bottle of oil I purchase. I would go the oil with the better specs, which in the example given by the OP, is the ST with the Dexos1 spec.