featured image maintaining diesel fuel

7 Things to Consider for Maintaining Diesel Fuel Systems

As the inventor of the diesel engine, Rudolf Diesel would be proud of the global acceptance and dramatic improvements made to the engine over the last century. Answering the ever-present need for lower fuel costs, diesel engines were developed to take advantage of the high energy content of diesel fuels. Very different from fossil fuels, diesel fuel has several properties that must be maintained to operate effectively in today’s modern diesel engines.

Today we’re going to talk about the first seven of fourteen of these characteristics of maintaining diesel fuel systems:

  1. Heat Value
  2. Ignition quality/cetane rating
  3. Viscosity
  4. Sulfur content
  5. Water and sediment content
  6. Carbon residue
  7. Flash point
  8. Pour point
  9. Cloud point
  10. Active sulfur copper strip corrosion content
  11. Ash
  12. Distillation
  13. Specific gravity
  14. Winter Fuel issues

1. Heat Value

A calorimeter is used to measure the heat value of diesel fuel and determines how much energy the fuel provides when burned. Basically, when a specific amount of diesel fuel is burned, the amount of heat is measured in British Thermal Units (BTUs).

  • The heat value of No. 2 diesel fuel is 139,500 BTUs per gallon
  • The heat value of No. 1 diesel fuel is 125,500 BTUs per gallon which is approximately 10% lower than that of No. 2
  • For comparison, the heat value of gasoline is 124,500 BTUs per gallon.

The higher the heat value is, the more the engine can generate power, which means using less fuel to do the same amount of work.

2. Ignition Quality/Cetane Rating

We measure the ignition quality of a fuel using the Cetane rating. The easier a diesel fuel ignites, and the manner in which it burns, impact engine starting and combustion roughness. Pure cetane is a colourless, liquid hydrocarbon with excellent ignition qualities and is rated at 100. The higher the cetane rating is, the shorter the lag time between the fuel entering the combustion chamber and when it begins to burn. Good quality diesel fuel with a high cetane rating has a lag time of approximately 0.001 second.


Cetane rating requirements depend on the design load and engine size as well as atmospheric conditions. For instance, engines operating at higher altitudes or lower temperatures require a higher cetane fuel to start and operate properly. Typical cetane ratings for No. 2 diesel would be 46 – 48. No. 1 diesel is usually about 51 – 53.

Note: Most filling stations do no provide the cetane rating of their fuel. Owners should purchase diesel fuel from a well-known source that is frequently utilized to ensure fresh fuel is being purchased.

Note: Modern diesel engines have a recommended cetaine rating of 40. A cetane rating above 48 is not recommended as it will not increase engine performance and could cause fuel knocking.

3. Viscosity

Viscosity is simply a way to measure the resistance to flow. As the temperature increase, viscosity. Fuel viscosity is an important factor in the operation in modern High-Pressure Common-Rail (HPCR) fuel system equipped engines.

Low viscosity fuel produces a fine mist of fuel which improves its mix with incoming air to encourage a complete combustion for better power and lower emissions.

High viscosity fuel typically has a heavier mist of fuel, resulting in hard starting and white smoke issues.

4. Sulfur Content

Because of increased wear and tear on pistons, rings, valves and cylinders, the sulfur content of diesel fuel has recently drawn a great deal of attention. This increased wear is due to the corrosive effects of hydrogen sulfide in the fuel combined with sulfur dioxide (or sulfur trioxide), formed during the combustion process. This wear and tear are less serious under constant loads and during high–temperature operation.

Some after-market companies offer fuel additives to make up for the lubrication lost by the reduced sulfur content of the diesel fuel. If your fuel quality is questionable, replace it with fuel from a known good source to ensure the fuel system components are not at fault.

5. Water and Sediment Content

Water and sediment content in the fuel can cause fuel system components to become rusty and damaged. The higher water content in a diesel fuel can cause iron oxide particles to form inside the fuel tank, causing internal rusting of fuel lines, pumps and injection components when the engine is not in use.

We’ve frequently come across this problem in engines that are put in storage in the fall, even though they were ‘running great all season’. When taken out again in the spring, the owner finds that the engine needs fuel system components replaced because of rust and contamination issues.

6. Carbon Residue

That black soot material you see after diesel fuel is burned is called carbon residue. The permissible amount of carbon residue deposits depends upon the engine manufacturer and the running conditions of the engine.

7. Flash Point

The flash point of diesel gasoline fuel is the minimum temperature the fuel must be heated before flammable vapour is produced and could ignite. The lower the flash point is, the higher the risk of explosion.

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