Well, since I don't live in the city, other than the school bus, which I use most of the time as well as my bicycle, public transportation is pretty much out of the question, otherwise I would primarily use that. And I guess what you define as Diesel's first engine is in question here. The engine presented at the Paris Exhibition in 1900 ran wholly on peanut oil. As for the fats and acids and other contaminants, aren't the fats also burnt, and the acids not significant if the oil's dry?

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1983 240D 3.0T 4-speed manual, now sold

1989 Subaru GL Wagon 5-speed Touring Edition