Sulfur is present in all crude oils and refined products. During combustion, sulfur compounds burn to form acidic byproducts, S02 and S03, which form sulfates in the exhaust gas stream. Depending on the crude source, diesel fuels contain various amounts of sulfur compounds, which yield corrosive sulfur oxides on combustion. These can cause high rates of engine wear and rapid depletion of engine oil additives. Engine manufacturers often relate oil change intervals to the fuel sulfur content.
All diesel fuels contain small amounts of water.
Hydrocarbon type and bulk temperature control the amount of water that a fuel holds. As temperature decreases, the amount of water dissolved in the fuel will also decrease and may lead to a water layer forming on the bottom of the storage vessel. To prevent bacterial contamination and the pumping of water into the fuel distribution system, draining the tank regularly should minimize this layer. Many diesel fuel treatments are offered to control water. These additives are very popular, especially in the trucking and marine industry.