Gasoline and diesel fuels contain sulfur as part of their chemical makeup. Sulfuric acid is produced when sulfur combines with water vapor formed during the combustion process, and some of this corrosive compound is emitted into the atmosphere through the exhaust.
Sulfuric acid is a major environmental pollutant, coming back to earth in contaminated rainwater. This 'acid rain' has been responsible for destroying or degrading vast areas of arable land.
As a result, the removal of sulfur from motor fuels has become a major part of most countries vehicle emission control programs.
High sulfur levels in fuel, when combined with water vapor, can also cause corrosive wear on valve guides and cylinder liners, which can lead to premature engine failure. The use of proper lubricants and correct oil drain intervals helps combat this effect and reduces the degree of corrosive damage.
Sulfur reduces catalyst efficiency in modern vehicles, and vehicles operating with higher sulfur gasoline have higher emissions than vehicles operating on lower sulfur gasoline.
There is evidence that in some instances, sulfur in gasoline may degrade the performance of oxygen sensors, which may also result in high emissions. High sulfur levels in gasoline may also impair the performance of OBD II systems on some vehicles.
Although regulations have reduced the permissible levels of sulfur in fuel, there are some side effects from using low sulfur diesel fuel.
The refining process used to reduce the sulfur level can reduce the natural lubricating properties of the diesel fuel, which is essential for the lubrication and operation of fuel system components such as fuel pumps and injectors.
Also, to reduce the sulfur content, oil companies change the overall chemical composition of the fuel and this can affect fuel pump seals, engine seals, and 'O'rings, some of which react to changes in fuel composition by swelling or shrinking.
This problem can be fixed by regular servicing and by replacing the seals with ones made from newer, less susceptible, materials.
