What Diesel Fuel Is The Best

Jake Mayock

Meet Jake

Jake is a founder of 8020 Media and one of the lead writers at DieselIQ. He has over 10 years of experience in the automotive industry and is the proud owner of a 2002 F-350 7.3 PowerStroke. When Jake isn’t working, he’s usually wrenching on his PowerStroke, single turbo BMW, or Miata track build. Jake delivers tons of knowledge and hands-on experience and is a valuable asset for those looking to take their diesel to the next level. He is highly knowledgeable on Powerstroke and Duramax diesels.

Diesel fuel is graded and designated by the American Society for Testing and Materials (ASTM), while its specific gravity and high and low heat values are listed by the American Petroleum Institute (API). Each individual oil refiner and supplier attempts to produce diesel fuels that comply as closely as possible with ASTM and API specifications. Because of different crude oil supplies, the diesel fuel may be on either the high or low end of the prescribed heat scale in BTU per pound or per gallon.

Because of the deterioration of diesel fuel, only two grades of fuel are considered acceptable for use in high-speed heavy-duty vehicles. These are the No. 1D or No. 2D fuel oil classification. Grade No. 1D comprises the class of volatile fuel oils from kerosene to the intermediate distillates. Fuels within this classification are applicable for use in high-speed engines in service involving frequent and relatively wide variations in loads and speeds. In cold weather conditions, No. 1D fuel enables the engine to start easily.

In summary, for heavy-duty high-speed diesel vehicles operating in continued cold-weather conditions, No. 1D fuel provides better operation than the heavier No. 2D. Grade No. 2D includes the class of distillate oils of lower volatility. They are applicable for use in high-speed engines in service involving relatively high loads and speeds. This fuel is used more by truck fleets due to its greater heat value per gallon, particularly in warm to moderate climates.

Even though No. 1D fuel has better properties for cold weather operations, many still use No. 2D in the winter, using fuel heater/water separators to provide suitable starting, as well as fuel additive conditioners, which are added directly into the fuel tank. 

Selecting the correct diesel fuel is a must if the engine is to perform to its rated specifications. 

Generally, seven factors must be considered in the selection of a diesel fuel:

  • Starting characteristics
  • Fuel handling
  • Wear on injection equipment
  • Wear on pistons
  • Wear on rings, valves, and cylinder liners
  • Engine maintenance
  • Fuel cost and availability

Other considerations in the selection of a diesel fuel are as follows:

  • Engine size and design
  • Speed and load range
  • Frequency of load and speed changes
  • Atmospheric conditions

Diesel Fuel Cetane Number

Cetane number is a measure of the fuel oil’s volatility; the higher the rating, the easier the engine will start and the smoother the combustion process will be within the ratings specified by the engine manufacturer. Current 1D and 2D diesel fuels have a cetane rating between 40 and 50.

Cetane rating differs from the octane rating used in gasoline in that the higher the number of gasoline on the octane scale, the greater the fuel resistance to self ignition, which is a desirable property in gasoline engines with a high compression ratio.

Using a low octane fuel will cause premature ignition in high compression engines. However, the higher the cetane rating, the easier the fuel will ignite once injected into the diesel combustion chamber. If the cetane number is too low, you will have difficulty in starting. This can be accompanied by engine knock and puffs of white smoke during warm-up in cold weather.

High altitudes and low temperatures require the use of diesel fuel with an increased cetane number. Low temperature starting is enhanced by high cetane fuel oil in the proportion of 1.5°F lower starting temperature for each cetane number increase.

Fuel Volatility

Diesel Fuel fuel volatility requirements depend on the same factors as cetane number. The more volatile fuels are best for engines where rapidly changing loads and speeds are encountered. Low volatile fuels tend to give better fuel economy where their characteristics are needed for complete combustion, and will produce less smoke, odor, deposits, crankcase dilution, and engine wear.

The volatility of a fuel is established by a distillation test where a given volume of fuel is placed into a container that is heated gradually. The readiness with which a liquid changes to a vapor is known as the volatility of the liquid. The 90 percent distillation temperature measures volatility of diesel fuel. This is the temperature at which 90 percent of a sample of the fuel has been distilled off. The lower the distillation temperature, the higher the volatility of the fuel.

In small diesel engines higher fuel volatility is needed than in larger engines in order to obtain low fuel consumption, low exhaust temperature, and minimum exhaust smoke.


The viscosity of diesel fuel is a measure of the resistance to flow of the fuel, and it will decrease as the fuel oil temperature increases. What this means is that a fluid with a high viscosity is heavier than a fluid with low viscosity. A high viscosity fuel may cause extreme pressures in the injection systems and will cause reduced atomization and vaporization of the fuel spray.

The viscosity of diesel fuel must be low enough for it to flow freely at its lowest operational temperature, yet high enough to provide lubrication to the moving parts of the finely machined injectors. The fuel must also be sufficiently viscous so that leakage at the pump plungers and dribbling at the injectors will not occur. Viscosity also will determine the size of the fuel droplets, which in turn govern the atomization and penetration qualities of the fuel injector spray.

Recommended diesel fuel oil viscosity for high-speed diesel engines is generally in the region of 39 SSU (Seconds Saybolt Universal), which is derived from using a Saybolt Viscosimeter to measure the time it takes for a quantity of fuel to flow through a restricted hole in a tube. A viscosity rating of 39 SSU provides good penetration into the combustion chamber, atomization of fuel, and suitable lubrication.


Lubricity is commonly defined as the ability of a fluid to minimize the degree of friction between surfaces in relative motion under load conditions.  When the lubricity is not at a satisfactory level, then many internal engine components including fuel pumps and injectors are prone to excessive wear and metal damage.  The results of such wear are inefficient performance, shortened service life and high replacement costs.

As the emission standards for diesel fuels have been decreased, the importance for adequate fuel lubricity has increased, since now critical engine parts must perform at evermore demanding operating pressures and temperatures and, consequently, with greater degrees of metal to metal contact.  Obviously, these factors explain why good lubricity quality is of prime importance to diesel engine owners.

Diesel Fuel Sulfur Content

Sulfur has a definite effect on the wear of the internal components of a diesel engine, such as the piston ring, pistons, valves, and cylinder liners. In addition, a high sulfur content fuel requires that the engine oil and filter be changed more often because the corrosive effects of hydrogen sulfide in the fuel and the sulfur dioxide or sulfur trioxide that is formed during the combustion process combine with water vapor to form acids.

High additive lubricating oils are desired when high sulfur fuels are used. Refer to the engine manufacturer’s specifications for the correct lube oil when using high sulfur fuel.

Sulfur content can be established only by chemical analysis of the fuel. Fuel sulfur content above 0.4% is considered as medium or high, and anything below 0.4% is low. No. 2D contains between 0.2 and 0.5% sulfur, whereas No. 1D contains less than 0.1%. Sulfur content has a direct bearing on the life expectancy of the engine and its components. Active sulfur in diesel fuel will attack and corrode injection system components and contribute to combustion chamber and injection system deposits.

What Is The Connection Between Sulfur And Lubricity?

There is a misconception that sulfur is what provides the lubricity to diesel fuel, but that idea is only indirectly correct.  Although the sulfur does contribute somewhat to lubricity, the lower lubricity level of low sulfur fuel is more a by-product of the refinery processes used for desulfurization.

No crude oil is entirely pure, it always contains trace amounts of various impurities.  One such common impurity is sulfur; depending upon the crude source, the sulfur content can range from as low as 500 ppm (sweet crude) up to as much as 10 fold (sour crude) that amount.

During the desulfurization process via hydrotreating, hydrogen gas is introduced to the crude under extreme temperatures and pressures.  The hydrogen combines with the sulfur to form hydrogen sulfides that are then removed and ultimately converted into elemental sulfur for resale. 

Unfortunately, during desulfurization, critical polar and organic aromatic compounds innate to the fuel and identified as responsible for imparting significant lubricity quality, are destroyed under the necessarily intense operating conditions.  The resulting yield is a satisfactory low sulfur diesel fuel, but also one that is unsatisfactorily low in lubricity.

Cloud and Pour Point

Cloud point is the temperature at which wax crystals in the fuel (paraffin base) begin to settle out with the result that the fuel filter becomes clogged. This condition exists when cold temperatures are encountered and is the reason that a thermostatically controlled fuel heater is required on vehicles operating in cold weather environments.

Failure to use a fuel heater will prevent fuel from flowing through the filter and the engine will not run. Cloud point generally occurs 9-14°F above the pour point.

Pour point of a fuel determines the lowest temperature at which the fuel can be pumped through the fuel system. The pour point is 5°F above the level at which oil becomes a solid or refuses to flow.

Cleanliness and Stability

Cleanliness is an important characteristic of diesel fuel. Fuel should not contain more than a trace of foreign substances; otherwise, fuel pump and injector difficulties will develop, leading to poor performance or seizure. Because it is heavier and more viscous, diesel fuel will hold dirt particles in suspension for a longer period than gasoline. Moisture in the fuel can also damage or cause seizure of injector parts when corrosion occurs.

Fuel stability is its capacity to resist chemical change caused by oxidation and heat. Good oxidation stability means that the fuel can be stored for extended periods of time without the formation of gum or sludge. Good thermal stability prevents the formation of carbon in hot parts such as fuel injectors or turbine nozzles. Carbon deposits disrupt the spray patterns and cause inefficient combustion.

How to Improve Your Diesel Fuel Quality

The life blood of your diesel engine is diesel fuel and the major enemy of fuel injection systems is poor quality fuel. From extensive research and testing, we have found that variations in fuel quality around the world can adversely affect today’s precision fuel injection systems. Poor quality fuel can cause performance issues, premature wear, gumming of components, and plugged filters. To resolve these issues and to provide protection of your fuel injection system, get a quality diesel fuel additive … there are many diesel fuel additives on the market. We choose Stanadyne Perfomance Diesel Fuel Additive because Stanadyne brand diesel fuel additives are the only ones in the world that are:

  • Developed by a fuel injection systems manufacturer
  • Tested and approved by major engine and vehicle manufacturers
  • Proven to perform best in independent tests

Stanadyne fuel additives protect and improve the performance of all fuel injection systems including:

  • High pressure common rail
  • Unit injectors
  • Rotary distribution pumps
  • In-line pumps
  • Multi-Port Injection

Stanadyne fuel additives comply with federal low sulfur content requirements for use in diesel motor vehicles and non-road engines.

All of Standyne Fuel Additives meet all engine fuel system requirements and will not harm exhaust after treatment systems such as Diesel Particulate Filters (DPF) or Selective Catalytic Reduction (SCR) systems.

Testing has shown an average fuel economy improvement between 3% – 4%, and in some cases as high as 10%. Actual savings will vary and are dependent on fuel quality, driving conditions, fleet and/or engine age and driving habits. 

Stanadyne Performance Formula protects your diesel engine and improves engine performance. The detergency and cetane improver in Performance Formula will help restore fuel economy, increase horsepower and torque. To help restore your engine’s maximum fuel economy, horsepower and torque as outlined above, use Performance Formula All Season or Warm Weather Blend with every fillup and treat with Performance Formula Injector Cleaner 4 – 6 times per year.

Stanadyne is a premium all-season, multi-function diesel fuel additive, designed to tackle virtually any diesel fuel related problem.

Benefits of Fuel Additives

  • Restores/Increase Horsepower – detergents clean deposits in the injection system resulting in improved combustion, better acceleration, power, and torque
  • Reduces Fuel Consumption – independent tests show an average of 4% improvement in MPG and gains up to 9.6%
  • Cetane Improver – improves combustion resulting in better engine starting, smooth running, and reduced engine noise
  • Meets all engine fuel system requirements – will not harm exhaust aftertreatment systems
  • Reduces Emissions – reduces Smoke and Particulates
  • Cleans and Protects – detergents and deposit modifiers help protect injection pumps, injectors, nozzles, etc.
  • Reduces Wear – lubricity improvers restore lubricity to ultra low sulfur and other low lubricity diesel fuels
  • Stabilizes Fuel – keeps fuel fresher and protects against formations of gums caused by oxidation
  • Cold Weather Protection – improves diesel pour point up to 40°F (22°C), and cold filter plug point by up to 25°F (13°C), depending on base fuel
  • Corrosion Preventative – Corrosion inhibiters will protect the fuel system from rust and corrosion
  • Helps Remove Water – special demulsifiers cause tiny water droplets to come out of suspension/emulsion, so the filter/separator can more effectively remove water
  • Contains No Alcohol – avoids corrosion and accelerated wear
  • Specially Formulated – for use with ultra low sulfur diesel fuel Can be used with Bio Diesel Fuel up to B20 (20% bio content approved ) – increased water separation shown in bio content up to B20

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    1. I was hoping this article would discuss the difference between brands like Sunoco, Shell etc and off brands at big box or truck stops. Supposedly the gas listed as top tier is better than non-branded.

    1. My Chevy truck dealer warned me not to use any fuel additives at all, that they will probably harm the engine. I am somewhat wary of this advice. I have never seen cetane numbers at any fuel station. How do you find them by brand?

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