Higher fuel system operating pressures, lower system tolerances, tighter filtration and the ultra-low sulfur requirements have pushed fuel cleanliness into the maintenance spotlight. Engine manufacturers are now recommending that diesel fuel that does not meet an ISO Cleanliness Code of 18/16/13 should be filtered before introduction to the fuel system. Injector manufacturers are mandating an ISO cleanliness code of 13/9/6 with water content levels at less than 200 ppm.