Now that I have the snow tires off and it's a bit warmer, I am definitely getting better mileage again. But not quite 15 km/L (~35 mpg). Still, I am driving 120 km/h every day for 150 km so 14 km/L isn't all that bad.

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1991 MB 300D 2.5 Turbo (207000km) (now gone)
1993 Audi 100 CS Quattro (300000km)
1999 VW Jetta TDI (290000km)
2002 Audi A6 3.0 Quattro (150000km)
2005 MB E320 CDI (34000km)