Diesel engines do inherently put out very high levels of NOx (relative to gasoline engines) and NOx's are the worst offenders when is comes to generating smog. If you are worried about your contribution to smog driving around in a 'dirty' diesel, make sure that at least your EGR is connected......lower combustion temps reduce NOx and that is why the EGR is there. On the plus side for diesels is greater efficiency so less fuel use and a smaller "carbon footprint"....but that doesn't necessarily mean less pollution of all types.

I don't think the EPA is biased against diesels, I think they just present the facts about diesel emissions but without painting an entire picture. The offset for drivers of old Benz diesels I think is how much pollution we are all preventing from being created by driving these cars that last 30+ years. No metal smelters belching who knows what all making steel to build cars on my account, no power plants burning coal and make electricity to run those smelters and those car factories on my account.

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1985 300D 231K anthracite grey w/black int.