1. As shipped 4.0T oil fill was apparently 504 spec. All 4.0T's, S8 or A8 (or S7 or S6) were shipped into USA with 504 oil--at least as of 2015 and assuming Audi wasn't pulling yet another stunt with the EPA. 504 oil would give them a better fuel economy result, so I could see why they might play games there, especially in the TDI fraud era. BUT, the deep dive EPA table says they were shipping the 3.0T with the more common 502 spec. EPA 2015 raw data table excerpt is below for those of you who want to see it first person. I included the D4 3.0T too so you can see they did differentiate fill by motor. For laughs I left in the MPG related detail--you can see how they round it; behind the scenes in the spreadsheet they also do some adjusting across all the vehicles to try to downrate the optimistic lab conditions to real world. Data comes from this page BTW: https://www.fueleconomy.gov/feg/download.shtml You download the "Datafile" version for a given year...and put your reading glasses on. I focused on 2015 since I own it. I recall from looking at more recent year data it also showed the 4.0T 504 fill info. Also, 504 is what they would be using in Euro petrol motors in general going back some years now, along with the variable and often longer intervals that rely on various algorithms and sensors to compute. Note the opportunity for more late found/hidden issues here at the manufacturer level, where the home country Vaterland cars and testing are not using the same oil spec as dealers and owners are routinely pouring into them here.

2. Dealer service is probably not 504 spec. Dealers do not seem to use 504 oil, at least not mine under AudiCare. I can see it from the part numbers on the invoices as well as the general spec. As a basic give away, if the fill is listed as a 5W40 it is probably the 502 spec oil, while if it is the 5W30 spec, it is more likely to be the 504 oil. As in, 504 oil is typically 5W30, while there are a variety of viscosities in 502. I can't be categorical given how varied the Audi oil approval listings are, particularly for 502.

3. 504 vs 502 technical advantages. I ran off the comparison graph again from the Lubrizol site that allows some oil spec comparisons. See below. (Higher spider graph results are "better" to be clear). What I did was take the leading German auto specs listed on a bottle of Castrol Professional 5W40 502 oil. That is the common dealer fill AFAIK, uV dye and all. They buy in big barrels though, so harder to really trace. To try to present in best light, I included the BMW and Mercedes specs that are also listed on the bottle. The tool notes though say those cross standards type comparisons (i.e. not just among the VW stds.) may not be representative. If anything, here the BMW and Merc. stds provided "better" results than 502 standing alone. In any case I ran all of these against 504 spec. I tred to use colors to delineate the most important and obvious 502 vs 504 spec differences, even in an oil might actually be higher quality in some ways like the BMW + Merc. specs help draw out. The difference is pretty obvious. Besides no brainers like fuel economy and wear, notice on these "turbo" type issues the areas that are helpful--less sludge, lower piston deposits, etc. Lubrizol tool is here if interested: https://online.lubrizol.com/relperftool/pc.html Discussed in threads on Bob is the Oil Guy forum for technical dive stuff, including nuances in these specs.

4. 504 requires ultra low sulphur gas, which needs to be checked at (USA) state level. The BIG catch: to use a 504 oil, you really need to be sure the gasoline you use is ultra low sulphur. I know CA is and has been for some years. It is also required in Europe, and related to why 504 oils are the norm there for new gas vehicles. It was unique in the USA though, and probably among the reasons Audi USA went slow on calling out the 504 spec in general. My casual understanding and memory is other states were supposed to have cut over to it (mandatorily) by a year or two ago. There are also murky EPA exemptions for small refiners that may go out some years still. But at a state specific level, the information is hard to come by and the deadline was delayed a few times along the way. I'm comfortable it works for me in CA, but would urge others to poke deeper in other states or local gas suppliers to get comfortable there, especially the non-"CARB" ones. That is, the ones not following the CA emissions rules--which is also apparently the tie in elsewhere in the thread to get comfortable the CA emissions warranty out to 7/70 covers the turbos. To anticipate, there is no magic "web list" (or YouTube video...) by state that I came across in the past. With the current EPA and administration uncertainties, the nebulous exemptions for some refiners, as well as history of postponements, in past I found it hard to really nail down. For deeper dive on the fuel compatibility problem, again search the specs and posts on the Bob is the Oil Guy forum. It has occasionally been flagged on AW too, at least in the D3 forum a few times.

As far as cost/price, at first i was able to get Castrol 504 dealer spec oil from audiusaparts in the $7 or $8/qt. range. But they stopped selling oil more recently. Last search turned up ECS as the likely cheapest in $9 range. Ebay ones are typically somewhat over $10 shipped. Thus yes, this is a fair amount more expensive than the 5 qt. jug or other Spring sale Mobil 1 0W-40 or Castrol Euro Formula 502 compliant oils. On the other hand, rounding error against turbo replace cost. I haven't poked recently, but generically an oil lableled "ESP" in the common brands may be a 504 oil, and it will typically be 5W30. You need to look at the labeling or Audi's 504 supplier spec sheet to be sure.

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