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Diesel 1 vs Diesel 2: What’s The Difference?

Selecting the optimal fuel type for a car can influence the performance and longevity of the vehicle’s engine significantly. This distinction is particularly relevant for diesel fuels like Diesel 1 and Diesel 2. So, what’s the difference between Diesel 1 and Diesel 2?

Diesel 1 is higher in quality than Diesel 2. Due to its high cetane rating, Diesel 1 combusts quickly and enables engines to start easier in low temperatures. Engines with Diesel 1 also function more efficiently and require less maintenance than those fueled by Diesel 2.

Diesel 1 or Diesel 2 have distinct physical characteristics and affect the operational efficiency and lifespan of engines differently.

To ascertain the appropriate grade for our engine needs, we must compare and comprehend the differences between Diesel 1 and Diesel 2.

Diesel 1 vs Diesel 2: A Comparison

Diesel (or distillate fuel oil) is graded according to its quality,  physical properties, and constituents.

ASTM International is the primary organization that sets the standards for grading diesel fuel. The grades indicate the lightness of the fuel and the parts per million of sulfur it contains (the digits after the letter S). 

There are seven grades of diesel within the ASTM system:

  • No. 1-D S15,
  • No. 1-D S500,
  • No. 1-D S5000,
  • No. 2-D S15,
  • No. 2-D S500,
  • No. 2-D S5000,
  • No. 4-D.

The most commonly used grades are No. 1-D (Diesel 1) and No. 2-D (Diesel 2). These grades are worth comparing because they have distinct characteristics and specific implications for engine functioning and maintenance requirements.

Let’s examine the differences that set Diesel 1 and Diesel 2 apart.  

Diesel 1 vs Diesel 2: Cetane Rating

The No. 1-D and No. 2-D grades of diesel have different cetane ratings.

Diesel 1

The cetane rating of diesel fuel indicates how quickly fuel ignites when injected into the combustion chamber.

Diesel 1 has a higher cetane rating than No. 2-D. Cetane ratings for Diesel 1 typically range between 45 and 55.

The difference between the cetane rating of Diesel 1 and Diesel 2 has implications for engine performance.

For example, engines with Diesel 1 start quicker than those fueled by No. 2-D because the grade is more flammable.

The quicker ignition time of Diesel 1 also enables engines to function more smoothly during operation than grades like No. 2-D.

Diesel 2

Diesel 2 has a lower rating than No. 1-D. The average cetane rating of Diesel 2 is between 40 and 42.

As a result of the lower cetane rating, Diesel 2 ignites more slowly than Diesel 1. Consequently, engines with Diesel 2 start slightly slower than those with No. 1-D.

Diesel 1 vs Diesel 2: Viscosity

Another fundamental difference between Diesel 1 and Diesel 2 is their density or viscosity.

Diesel 1

As noted earlier, the grading of diesel indicates its lightness or heaviness, which are industry terms that describe how dense or viscose the fuel is. Diesel 1 is the lightest grade and is called a light to middle distillate fuel.

The low viscosity of No. 1-D means this grade of diesel moves more fluidly through the fuel system which increases the engine’s overall operational efficiency, while also providing benefits in colder climates (more on this later).

Diesel 2

Diesel 2 is heavier than Diesel 1 and is considered a middle distillate fuel.

The higher viscosity of Diesel 2 has the advantage of increasing the fuel’s lubricating effect within the engine.

However, the increased viscosity of No. 2-D means this grade does not flow as smoothly through the engine as No. 1-D. In cold conditions, Diesel 2 tends to thicken into a gel-like substance which impedes its passage through the engine’s fuel system.

Diesel 1 vs Diesel 2: Additives

One of the principal distinctions between No. 1-D and No. 2-D is the number and types of fuel-enhancing additives in each grade.

Diesel 1

Diesel 1 And Diesel 2 contain additives such as lubricants and detergents. However, Diesel 1 also has some additional constituents that No. 2-D does not.   

Diesel 1 has added chemical constituents that improve the fuel’s cleanliness and lubrication and reduce its corrosive effects on engines.

Two of the engine-protecting additives in No. 1-D are:

  • corrosion inhibitors,
  • demulsifiers.

The corrosion-inhibiting chemicals in Diesel 1 reduce the abrasive and rusting effects of sediments that accumulate in pipes and other components of the engine’s fuel distribution system.

Diesel 1 also contains demulsifying agents. Demulsifiers isolate emulsified water from the fuel. This separation expedites the removal of the water from the fuel system, which is crucial for preventing severe engine problems.

Diesel 2

Diesel 2 generally has fewer fuel-enhancing additives than No. 1-D.

The common additives in Diesel 2 include chemicals that decrease the fuel’s viscosity to enable easier engine starting in low-temperature conditions. For instance, Diesel 2 has a higher wax content than Diesel 1, so the fuel often contains chemicals that prevent the accumulation of waxy sediments in the fuel system.

No. 1-D is often added to Diesel 2 to improve the starting time and operational efficiency of engines in cold conditions.

Diesel 1 vs Diesel 2: Engine Wear

Diesel 1 and Diesel 2 impose differing amounts of wear and tear on engines.

Diesel 1

Diesel 1 is generally more gentle on engines than No. 2-D. The high viscosity of Diesel 1 enables it to pass smoothly through the engine’s fuel injection and distribution components.

No. 1-D also reduces the amount of wear on engines because of the fuel’s low wax content and anti-corrosive and de-emulsifying additives.

In addition, Diesel 1 prevents excessive wear due to its high cetane rating, which enables shorter ignition delay times, and smoother, more efficient engine functioning.

Consequently, engines with Diesel 1 require less maintenance and have longer lifespans than those with No. 2-D.

Diesel 2

Diesel 2 causes more wear and tear to engines compared with No. 1-D, though the difference is not dramatic and only becomes a significant factor when considering the overall lifespan of the engine.

The high viscosity of Diesel 2 requires more energy to move through the fuel system, so this grade of diesel places more strain on engines than Diesel 1.

The lower number of fuel-cleaning de-emulsifiers and anti-corrosion additives in Diesel 2 might also contribute to relatively higher degrees of wear and tear compared to No. 2-D.

However, it is crucial to emphasize that the viscosity of Diesel 2 makes the fuel more lubricating. The extra lubrication of No. 2-D mitigates the wear on the engine by reducing friction in the fuel injector and pump.

Diesel 1 vs Diesel 2: Noise

Different grades of diesel produce varying levels of engine noise.

Diesel 1

Diesel 1 is less noisy than No. 2-D.

The noise occurs during the fuel ignition process. When the fuel ignites and vaporizes, it mixes with air in the combustion chamber and becomes extremely hot. The heat of the diesel fuel causes a dramatic increase in pressure, resulting in a loud banging noise.

Due to Diesel 1’s high cetane rating, the fuel ignites rapidly. This quick ignition time means there is less time for the vaporized fuel to mix with air, which reduces the characteristic knocking sound associated with diesel engines.

Diesel 2

Engines with Diesel 2 tend to make more noise than those with No. 1-D.

The lower cetane rating of Diesel 2 means the fuel takes longer to combust. As a result, No. 2-D remains in the combustion chamber for a longer period than No. 1-D, so higher levels of heat and pressure accumulate, increasing the volume of the noise produced when the engine is operating.

Diesel 1 vs Diesel 2: Fuel Economy

Fuel economy (or output per volume) is a critical distinction to consider when comparing No. 1-D and No. 2-D.

Diesel 1

The fuel economy (measured in miles per gallon) of Diesel 1 is marginally less when compared with No. 2-D. However, engine condition and specifications usually have a larger influence on fuel economy than the grade of diesel.

Nonetheless, fuel economy ratings derive from the heating value of a particular grade of diesel. Since No. 1-D is a lighter grade than No. 2-D, the fuel has a lower heating value. Consequently, Diesel 1 has a lower fuel economy rating than No. 2-D.

Diesel 2

In comparison, Diesel 2 has a superior fuel economy rating to Diesel 1 due to its higher heating value.

As a result, No. 2-D enables cars to travel more miles for each gallon of fuel in the tank than No. 1-D.

Diesel 1 vs Diesel 2: Smoke Emissions

The grade of diesel partly influences the amount of black smoke that diesel engines emit.

Diesel 1

Diesel 1 emits less smoke than Diesel 2.

Engines release smoke from their exhausts when diesel injects into the combustion chamber and does not burn completely. The rapid ignition of high cetane No. 1-D means there is less partially combusted fuel to create smoky exhaust emissions.

The lower levels of wax and anti-corrosive and de-emulsifying additives in Diesel 1 also produce cleaner exhaust emissions with fewer smoke-causing contaminants.

Diesel 2

Diesel 2 typically results in smokier exhaust emissions than Diesel 1.

The lower cetane rating of No. 2-D means this diesel grade takes longer to ignite in the combustion chamber, leading to the accumulation of fuel that is not combusted. As a result, No. 2-D is more prone to creating smoky emissions than No. 1-D.

If your diesel engine releases white smoke, the fuel isn’t burning the way it should. You can learn more about that in this post.


Diesel 1 (No. 1-D) and Diesel 2 (No. 2-D) are distinct grades of diesel fuel. Compared with Diesel 2, No. 1-D is a lighter diesel grade and has a higher cetane rating so it ignites quicker, and enables engines to start easier in cold temperatures. Diesel 1 also has more fuel-enhancing additives and causes less engine wear than Diesel 2.