The fuel of today is not what it was in the past in terms of composition, quality, and design. Fuel distribution capacity is decreasing while demand is increasing.  Most modern fuel is manufactured to be consumed within 30 days or less, which is further impacting the storability and stability for those with emergency backup generators. Other problems include water, contaminates, degradation, renewable fuel sources, and technology changes in modern diesel engines.

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Diesel fuel is hydroscopic; it attracts and holds water which is the biggest problem facing long-term storage of fuel. Think of it like the atmosphere in that when it has attracted enough moisture it will rain or drop to the bottom of the tank in the form of free water.

Effects of water on your system:

  • Promotes the formation of gums & varnishes
  • Develops acids
  • Accelerates the formation of bacteria/fungi/algae
  • Causes accelerated maintenance issues and corrosion

There are two main types of water in your fuel systems:

Absorbed Water

Diesel fuel passes through the distribution chain so fast that the water used in manufacturing does not have enough time to fall out to the bottom and be removed. This means that the fuel you are receiving can have a higher absorbed water content which is adding to the stability problems with storage. 

Ultra-Low Sulfur Diesel (ULSD) fuel can hold up to 2/10th of 1% water absorbed within the fuel mixture, whereas Bio-Diesel fuel can hold up to 1% water absorbed within the fuel mixture.

Free Water

The water that falls out of solutions (absorbed) to the bottom of the tank.  The higher the temperature, the more water it can hold.  This is more of a problem with Aboveground Storage Tanks (AST) than with Underground Storage Tanks (UST).  Free water will increase degradation, cause engine damage, enhance corrosion and promote bacterial growth.

Contamination is an important element in keeping your system running smoothly and cost effectively.  There are some essential things to watch out for, especially with the newer gensets and that is particle count. 

Particle count limits are set by your genset manufacturer due to technology changes that will cause catastrophic failures and potentially void your genset warranty which could reach costs in the millions not to mention loss of revenue.

Other forms of contamination include:

Dust and Dirt

Dust and dirt can get in anytime the fill port is open, such as during fuel transfer or inspections.

Dust and dirt will mix with the fuel and can become ingested into the fuel lines  where it can cause issues with:

  • Abrasion
  • Clogging
  • Injector damage
  • Lead to premature wear
  • Ultimately catastrophic engine failure.


The EPA mandated the significant removal of lead from gasoline and sulfur from diesel fuel, which was a natural poison for bacteria and/or microbes. 

Manufacturers use powerful chemicals to strip the sulfur from the crude oil which, in turn, removes some of the metals and other useful components.  These chemicals also decrease lubricity and other functions of the crude oil. 

Removal of the sulfur is one of the primary causes for the significant increase in biological/microbial growth in the fuel storage tanks, it is also the reason for the increase in the microbiologically influenced corrosion (MIC).

Renewable Fuel Sources

Bio diesel is affecting stability and storability of diesel fuel; it is also affecting wear and maintenance on the engines.  Manufacturers of diesel fuel do not need to notify the consumer of the amount of biomass in the fuel if it is less than 5%.  The biomass provides a food source and hospitable environment for bacteria, algae, and microbes to thrive.  The biomass itself can provide large enough contaminates to affect performance in some engines.

Bacteria, Algae, and Microbes

Bacteria and microbes need two things to survive and thrive; oxygen and food. They grow and live in the boundary area between the free water and the fuel. As the bacteria/microbes feed and grow they give off acid which accelerates further degradation of the fuel. As the bacteria/microbes die the carcasses fall to the bottom of the tank, under the water layer and form sludge. This leads to the fuel having high acidity which enhances corrosion as well as enhances rust, sludge, and other contaminates entering the fuel system causing catastrophic engine failure that is not covered by warranty due to particle counts.


Wax occurs when the fuel temperature drops and the water and other components in the fuel begin to gel up and eventually turns to a semi-solid.  Paraffin wax occurs naturally in all crude oils; the amount depends on the specific crude oil from which it was produced and the type of processing.  As the fuel is cooled it will start to become cloudy, this is when the wax begins to come out of the solution which is called the cloud point.  If the fuel is continued to be cooled it will reach a point where it will no longer flow and the wax will plug the filters and lines, this is referred to as the pour point or gel point. The pour point or gel point occurs about 6 to 10 oF below the cloud point.

High Pressure Common Rail Engines

Today’s engines feature the High-Pressure Common Rail (HPCR) engines that operate with pressures over 24,000 psi and with injector nozzle diameter of 2-3 µm.  They cannot handle the contaminates and water as with the old systems.  You can see premature issues with HPCR in the fuel injector nozzle holes and in the valves.  Blockage, corrosion, melting, and failure to atomize the fuel.  It is imperative to keep the fuel clean and dry.

There are viable solutions for addressing fuel quality issues…

Fuel Services Group uses a blended approach to maintaining fuel quality that is contained within our comprehensive fuel and tank maintenance program.  Our program is specifically designed to target every portion of your fuel and storage tank that will cause risk to your organization and increase your ROI.