You've kinda got it backwards. It's a forward compatibility problem, not a reverse one. By govt. mandate, diesels built after January 2007 are designed specifically to run on LSD or ULSD. Most diesel fuel sold in the US has already been LSD for awhile, which is Sulfur<500ppm. ULSD is Sulfur<15ppm or less. Anyway, newer diesels (post '07) are required to carry pollution control equipment and are required to have different valve and fuel rail designs, to lower their emissions. In these engines, running anything but LSD or ULSD will cause damage. However, you can certainly run a pre-ULSD mandate diesel on LSD or ULSD with no problems. Just make sure you change your fuel filters when you switch over, since ULSD has detergents in it and any leftover deposits from the old fuel will start coming loose. So in a nutshell: Old fuel will damage the new engines, but new fuel won't damage the old engines.