North American emissions are stringent when it comes to diesels. That may be something keeping ultra efficient diesels from the U.S. The new VW TDI's have post combustion injection to burn off nitrous oxides and other emissions when the fuel & exhaust gasses hit a catalytic converter like exhaust contraption. Hurts fuel economy for the sake of emissions. So some diesels, even if the manufacturer wanted to bring them to the U.S. would have to be reworked for better emimssions, which might make them less efficient, thus loosing some apeal.

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1984 300sd auto with 246,000 miles