Mine is somewhat dirty at changes, it is not pitch black, but it is noticeably darker.

I use Mobil 1 15-50 and change every 3750 miles.

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Ali Al-Chalabi

2001 CLK55
1999 Dodge Ram 2500 Cummins Diesel
2002 Harley-Davidson Fatboy
Merlin Extralight w/ Campy Record