I saw recently that there are more grades of diesel fuel than what is available at the pump, such as 4,5 and 6 used in large locomotives, turbines, etc. Does anyone know the difference between these grades and reg road diesel?

 

Diesel fuels are covered by the ASTM D975-04a specification, which describes seven grades of diesel:


[Grade No. 1-D S15, a special-purpose, light middle distillate fuel for use in diesel engine applications. Higher volatility than that provided by Grade No. 2-D S15 fuel. Maximum sulfur content 15 ppm.


Grade No. 1-D S500, a special-purpose, light middle distillate fuel for use in diesel engine applications. Higher volatility than that provided by Grade No. 2-D S15 fuel. Maximum sulfur content 500 ppm.


Grade No. 1-D S5000, a special-purpose, light middle distillate fuel for use in diesel engine applications. Higher volatility than that provided by Grade No. 2-D S15 fuel. Maximum sulfur content 5000 ppm.


Grade No. 2-D S15, a general-purpose, middle distillate fuel for use in diesel engines, especially in applications of varying speed and load. Maximum sulfur content 15 ppm.


Grade No. 2-D S500, a general-purpose, middle distillate fuel for use in diesel engines, especially in applications of varying speed and load. Maximum sulfur content 500 ppm.


Grade No. 2-D S5000, a general-purpose, middle distillate fuel for use in diesel engines, especially in applications of varying speed and load. Maximum sulfur content 5000 ppm.

Grade No. 4-D, a heavy distillate fuel, or a blend of distillate and residual oil, for low- and medium-speed diesel engines in applications involving predominantly constant speed and load.

Heavier fuel oils Grade 5 and 6 (residual), which are used primarily for heating purposes, are described by ASTM D396.

Find more info here. http://www.dieselnet.com/standards/fuels/us.html

 

There was also once a grade 3 diesel that is no longer in use. Canada has some other system for classifying diesel.