I came across this forum by accident and am very glad to have found it! I have a 2007 MB GL320CDI and have been going crazy trying to find pure diesel. One by one, all of the stations in the NW Chicago suburbs have converted over to bio. The last holdout, Mobil, is now going bio as well.
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Here is my contribution to the effort. I'll continue posting as I find stations or as stations convert over.
Waukegan: The Murphy by Wal-Mart in Fountain Square Plaza had bio, then it didn't and now the blue sticker is back again.
Lake Forest: One of the last holdouts, the Mobil station at the I-94 oasis, has now converted to bio. There is a VERY small blue sticker on a hard to see area of the pump.
Vernon Hills: The Mobil on IL-21, across from Ernie's Shell, has pure diesel and has always had pure diesel. Ernie's Shell does not have a blue sticker so perhaps it's OK but I have no idea. The Mobil on Route 60 and Butterfield has bio, along with a huge sign on the pump saying this is not a MObil branded product.
Libertyville: As noted by cmeller, the Shell on Peterson has NO stickers of any kind, not even the green ULSD sticker. The attendant had no idea what kind of diesel they sell. Last I saw, the Citgo on Peterson and Route 21 has bio.
Mundelein: The Clark on US 45 and Hawley had pure diesel until they closed. The station has now re-opened as a Mobil and they have NO stickers on the pump. The Shell that's about 2 blocks south of the new Mobil has bio. The Citgo on Route 45 and Route 176 has bio. So does the Citgo on Butterfield and Allanson.
Grayslake: The Thorntons on Route 45 and Washington has bio and so does the Thornton's on Hainesville Rd and Washington in Hainesville.
In summary, the only station on this list that I have
complete confidence about carrying pure diesel is the Mobil on Route 21 in Vernon Hills. This is pretty much the last Mobil station not to use bio, so I'm guessing its days are numbered.
I wonder how many people just fill up with whatever is available and have NO IDEA they are not supposed to be using bio. I really think those of us on this forum and other like-minded people are in the minority. It seems like Mercedes is starting to have issues in the Chicago area because they recently distributed a service bulletin to dealers instructing them how to identify bio-related sludging and other issues. MB dealers also test the fuel in the tank when these types of issues appear. If the tests confirm bio, then warranty service is denied. I would imagine that VW and Audi dealers are doing something similar, or soon will be.