Honestly I've been registered on bobistheoilguy for years I suppose, but just never think to "stop by" and see what's happening.
I'm enjoying this discussion, and can offer a couple of weblinks that you all may or may not appreciate, but I found them quite informative.
Also, right up front, please don't beat me up unnecessarily
, I am not an Audi owner and certainly know nothing about any possible risks you may encounter if you deviate from any exacting specifications of oil in your application. The bottom-line basic facts of motor oil engineering
is not "vehicle brand specific." However, yes it is true we all must be sure to comply with
the specific manufacture's absolute requirements. (In my case the absolute requirement is GM Dexos 1 Gen 2.) -sorry, I'm not yelling, just emphasizing key points-
To "BrandonT", I offer this: After one of my last UO analysis reports, I was rather unhappy with the viscosity at 100c being substantially lower that what I'm comfortable with. And similar to your results, my report did show a "trace" of fuel, but nowhere near the "allowable" limit. I now suspect it may be directly related to molecular "shearing" of the "long chain" viscosity improver additive.
That set me off on many hours of research (and posting a question on another forum) as to whether or not a 0W30 oil would be better than 0W20. -seems to me it would still give me the same winter temp/cold start protection, but the bonus should be significantly better high temp protection, and hopefully better wear protection. -and BTW, I have still not decided what I'm going to do. I still have a lot of warranty left, which I'd rather not risk. However, I seriously doubt using 0W30 vs the 0W20 would even be detectable in my case. (non-Audi, sorry, but the same motor oil-related engineering principles apply,,,)
So the first weblink deals with high temp high shear Standard ASTM D-4683 and other standards including SAE J-300, and many other ASTM D xxxx x standards. With two apologies:
One, the dissertation is quite lengthy, and two it is from a Corvette owner, which I hope is not "fighting words" for you, or will be unnecessarily painful otherwise. Personally, for my needs, I found the last several paragraphs to be the most valuable. https://www.corvetteforum.com/forums/c5-tech/4496042-engine-oil-shearing-and-specs-explained.html
With appropriate apology, the second link is to a specific motor oil manufacturer's site, but the dissertation does a good job
of explaining the factual basics of base stocks and additives. It certainly makes obvious the extreme advantage of a "Group IV" base stocks. A key statement in that article is that some synthetic base stock oils (Poly Alpha Olefins – PAOs and Esters) have such high natural Viscosity Indices that little if any additives are needed to achieve the multi-grade finished product. That link is: https://thelubepage.com/amsoil-maga...m-and-synthetic-oil-base-stocks-and-additives
Hey, I hope you all find the above informative, and hopefully even useful.
Okay, one last thing: Oil Film Strength.
This is likely an extremely important (maybe the most important?) factor in the interest of good engine wear protection
for all motor oils. And by that, I mean the specific value measured in pounds per square inch at which any specific motor oil fails. And that can only be determined with very specific laboratory equipment using exact controlled standards by an "independent party." (BTW, I can offer a link to one of those too, if anyone is interested,,,)
I just LOVE the following statement of basic lubrication fact:
"In any lubricated assembly employing two metal surfaces, there will not exist any wear of those surfaces as long as the surfaces never physically contact each other. Specifically when a sufficient boundary layer of lubricating fluid is continuously maintained, there is no foreign particle present larger than the clearance between the parts, AND that boundary layer has a film strength which exceeds the highest mechanical force attempting to make the two metal surfaces contact each other."
And of course, in the case of automotive engine oil, many other factors are important too. Like all of the important additives, like detergents, anti-corrosives, dispersants, acid neutralizers, anti-wear, etc. etc.
At this point for me, I am going to seriously consider using a synthetic oil with Group IV base stock. -and at this point, I'm only aware of a few brands. Also, I believe a 0W30 very obviously provides better protection at normal operating (hot) oil temperatures. AND, of course, it always goes without saying, using a correct high quality oil filter, and changing the oil religiously.
Cheers Everyone !!