Originally Posted by PandaBear
Typically, when people ask me question like this, I assume they are using the same oil between 2 grades as a comparison. They are not asking syn vs dino, or QS vs Valvoline, or even Mobil1 AFE vs EP vs HM, or even Ravenol ECS vs SFE. I assume this is a pretty straight forward apple to apple comparison.
You can always pick corner cases and just make every single question an "it depends" argument, and you get nothing out of any question or answer.
Given the myriad examples presented, this is hardly a "corner case". The answer is: Look at the bloody Noack, if it's available, and make an educated decision, it's really that simple. Why make sweeping generalizations when one can instead advocate for furthering one's knowledge?
Anyways, that would be a naive assumption. If somebody wants something "better" than dealer bulk 5w-20 or some other generic 5w-20 and they want to go to a 0w-20, that 0w-20 is going to be synthetic and your original statement, indicating that Noack would be an issue, would, typically, not apply in that scenario. For example, our RAM would have come filled with lord knows what 5w-20. The dealer services (for free) with bulk 5w-20, I've chosen, instead, to service with M1 EP 0w-20, which should be similar to the Ravenol product, given the PAO content. In this case, the selection of a 0w-20 would be a Noack upgrade, and it would be for most people going from bulk dealer 5w-20 to a synthetic 0w-20 unless that 5w-20 happened to be one of the very few with an extremely low Noack.
In the case of the OP, he was asking about swapping out dealer bulk 5w-20 with Supertech Synthetic 0w-20, which, in the worst case, would likely have the same Noack as the bulk product. Supertech "High Mileage" 0w-20 has a Noack of 10%, for reference. In most likelihood, the Supertech 0w-20 is an upgrade in Noack here.