ULSD has some goods and some bads... The sulfur compounds that were in the old 500 ppm diesel are the very hard/expensive to remove compounds... the ones that hydrodesulfurization cannot easily get to due to stearic hinderance... these are very refractory compounds such as 3,7 dimethylbenzothiophene and 4,6 dimethyldibenzothiophene. These compounds are aromatics and polyaromatics, and it was their aromatic structure that made them good lubricants. Now, that said, their aromatic structure also made them coke precursors, which caused all the soot and black smoke. This doesnt mean that an old diesel won't still make black soot and lots of particulate exhaust, but it does mean that newer diesels with tweaked combustion setups will be able to produce much less PM than their precursors, and also utilize catalyzed exhaust systems to clean up after themselves - something that wasnt possible with sulfur in the exhaust at high levels.
So, all of that said, ULSD should be a slightly better burning (if youre lucky, you might see a tiny increase in economy), but less lubricious fuel. Lets not forget that the trucing industry uses a LOT of fuel, and has their standars for fuel quality characteristics... Id venture to guess that some fuels are already additized to some extent. I always liked gulf oil's dieselect, and it gave slightly better performance and economy than other brands (this was pre-ULSD), as they claimed that they already additized it.
But additives from a corporate sense are hit or miss, so you do ned to take a preemptive stance for diesel and gasoline, IMO! FP60 is a great place to start for an all around, fleet use product. Likely MMO, Pwer service, and the Schaeffer's products are all really great.
Good luck!
JMH
