For the best in MPG go for 03-below pre-PD TDI's. They were the best in MPG, the 04-present are the new PD "pumpe duse" injection system like the passat TDI we have and dont get as good of fuel mileage without working for it.

The pre-PD TDI's can get 45mpg even if you drive them fast on the freeway.

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Current:
05 E320 CDI
07 GL320 CDI
08 Sprinter
05 Dodge Cummins
01 Dodge Cummins

Previous
2004 E55 AMG
2002 C32 AMG (#2)
1995 E300
1978 300D
1987 300D
2002 C32 AMG(blown motor :[
1981 300SD
1983 300SD
1987 300SDL
2002 Jetta TDI
1996 S420
1995 S500
1993 190E 2.6
1992 190E 2.3
1985 190E 2.3 5-Speed