Supposedly the rubber seals in the fuel system on the 606s are not bio safe. There's a whole viton seal upgrade that would need to be done.

As far as performance, I can tell you that they love bio just like every other IDI diesel.

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Current fleet
2006 E320 CDI
1992 300D - 5speed manual swapped

former members
1984 300D "Blues Mobile"

1978 300CD "El Toro"