Added a 16-oz bottle of 2-cycle oil to a full tank on the SD, and it works for me! After about 50 miles of driving, the car is quieter at idle, and seems to be getting better fuel economy (we'll see). But it is DEFINITELY quieter at idle. I'm still using the old 500ppm fuel, so I only added 16 oz as opposed to the prescribed 1 oz for each gallon.....When I start using the ULSD, I'll add a greater concentration!

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2015 E250 Bluetec Black/designo Sand
2014 GLK250 Bluetec Iridium Silver/Almond
1999 E320 Sedan Bordeaux Red/ Parchment
1999 E270CDI Estate Black Opal/Black
1983 300SD Champagne/Palomino Leather
1982 300SD Silver Blue/ Pacific Blue Leather