Diesels are to me more than just efficiency, good thing since diesel fuel is still too high.
When I pull in with my Mercedes diesels and people think that they're gas engines because they're so quiet (and most people think that they all sound like Dodge/Ford/GM pickup trucks) and don't smoke even at full-throttle. Besides that, my '87 300D is faster than my '94 E 320 (top end), and just loves to run. I've been considering having a hat made that says "Real Mercedes don't have spark plugs", I used to have a similar hat for the Hummer.
We'll have to see what happens with fuel prices regarding the economy of buying one in the US, last stats I saw still put Europe at nearly 70% of new vehicles sold are diesels. We aren't able to buy most of those engines here (such as the E 430 diesel which is amazing).

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Gone to the dark side

- Jeff