While I understand the importance of NOACK values being low, I often wonder what the 'real-world' impact is, for most vehicles.
I say this because, even though I've used plenty of oils with a NOACK in the 12+ range in my Fusion, I never notice any measurable drop in oil levels after a 7500 mile OCI. If NOACK is 12%, shouldn't that mean that if it really had an impact, I'd expect to see my oil level drop by some noticeable portion of 12% after 7500 miles?
I've run lots of 7500 mile oil changes, and I've never seen it drop by even a tiny amount.
... I think Virtus Probi got it right - The actual amount of time the oil in most engines actually spends anywhere near that 250C temperature is actually quite low. I'd say it spends most of its time at or below the average coolant temperature, which in my Fusion is about 200-202F... less than half of the 250C figure used in NOACK tests.