Removing the sulfur from 500 ppm (parts per million) to only 15 ppm was a very good thing to do. However, the sulfur served as the lubricant in the diesel fuel. Therefore engines using only ULSD diesel will be subject to much higher wear factors. Fortunately a biodiesel blend as low as 3% can replace the lubrication removed from the ULSD. Much better, though, is to use at least a B20 blend which provides the engine with 20% to 50% better engine lubrication and protection than pure ULSD. This is especially important with newer diesels which have high pressure injection pumps which are subject to very high wear factors. .