When I had a near new S4 V8 in '05, used Amsoil Diesel 15-40 AME in it at 4-6K intervals. I am fantatical about service and pay close attention to how the oil looks, among other things. Anyone with the timing chain motors know how bad it can look with metal particles. I see that all the time with customer cars, whether Audi or BMW.

The diesel oil did a great job protecting the S4 motor.

Due to the turbochargers on the BCY, I use Amsoil 5-40 Euro EFM full SAPS additive oil (for Euro spec oils anyway. About 75% of levels offered in other Amsoil lubes). it is rated for both gas and diesel engines. And with the new 5-50 Signature Series might give that a try, especially for summer use.

Last time I peered into the cylinders with a boroscope, it was extremely clean. The low burn-off (NOACK spec) I think was partly to thank. And the fact these cars have oil coolers, which drastically helps. Overall, to me, theres more to oil than it's ultimate PSI rating. That's great for extreme situations. Based on what I see day in, day out, years in years out and over the decades, we need an oil that excels in several areas-- again not just in PSI loading. It has to last and resist burn off and keep PH in check. The oil temperature issue

While I prefer Amsoil, have also used other top tier brands, going back to the late 80's when Castrol let me down. And Redline stepped in.

The oil debate will never cease....

I think one would have to do some extensive batch testing with UOA to truly quantify things. Or like what Amsoil does: takes engines apart and sends them out for 3rd party assessment. Not that they are the "best" in every category, but it's great to see a company lay it on the line with real world testing. Amsoil is a family run business, small for a petroleum manufacturer, and gets to pick exactly what to use in it's oil. From what I see they do a great and consistent job all all price points. They side step the advertising hype and let the products, tests, and racers speak. Cool in my book.