Don't overlook the earlier post about biodiesel. If you run even a blend of biodiesel, or even 20% used, filtered cooking oil, you'll get an immediate reduction in particulates. My 300D used to smoke pretty well under heavy load. I can't see any smoke in daylight under same conditions now. That's on 20% blend of used cooking oil /or/ 100% heated used cooking oil.

Really quick and easy fix? Pour a few gallons of NEW cooking oil right into your diesel tank to get a 20% blend. No filtering hassles and no problems with cold starts (it's been 5 degrees here and no problems at 20%).

Try it. It's cleaner, the engine will run quieter, and no work is required.

..on the subject of diesel particulate, I agree that it is less toxic than typical gas engine exhaust, but it isn't harmless. Less is better - within reason - especially when we can grow the cleaner fuel right here.

Gotta go hug a tree..!