My latest trip got me 31 mpg or about 13.1 km/L with about 100km city driving and 700km highway. Not as good as I was hoping.

I made a conversion web page because I was always getting tired of guessing approximate conversions in my head. The URL is below. I hope some other people find it useful. You can go either way (MPG to km/l and back again).

http://www.vangeyn.net/mpg/

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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)