I have been using HSD 2000ppm sulphur in my tractor for 4 years. I had an issue once with incomplete combustion causing light blue smoke. It has not happened since. I also use Optilube Ag formula in all my fill ups. I now have an excavator with a 55hp Yanmar tier 2 engine which means it has zero emission controls. For some reason when I use the HSD it will run with a light blue haze in the exhaust. My tractor does not do this. The fuel is from the same tank and is free from algae and filtered with a water separator 10 micron filter. The tank is stored indoors. What would cause this incomplete combustion? The engine starts and runs great either cold or hot.