Q. What is the shelf life of Diesel Fuel and how fast does it degrade?

A. – The shelf life if Diesel Fuel is from 1-2 years; under the best of conditions i.e. minimal exposure to water, air, and microbial contaminants.

University of Idaho Study –
Diesel Fuel can degrade as much as 26% in the first 28 days after it leaves the refinery.

Diesel Generator Failures, David Eoff, Preferred Utilities – Power Engineering Magazine August 2007
Diesel Fuel is an organic, refined product. It begins to decay as soon as it is refined.

NFPA 110 – Standard for Emergency and Standby Power Systems; – Fuel should be consumed within the storage life or provisions shall be made to
remediate fuel that is stale or contaminated replace stale or contaminated fuel with clean

Cummins Power Generation Power Topic #7004 – White Paper by Timothy A. Loehlein (2007)
Maintenance Schedule suggests water to be drained from tank weekly and to change fuel filters every 6 months. Also, Diesel Fuel is subject to contamination and deterioration over time and one reason for regular generator set exercise to use up fuel over the course of a
year before it degrades.

Q. What makes Diesel susceptible to degradation?

A. -

  • Age – it has a short shelf life
  • Water – water condenses on the walls of the tank due to temperature fluctuations throughout the day – especially in warm humid environments like South Florida.
  • Microbes – bacteria, algae, and fungi can flourish in the area where the water and the fuel meet (fuel / water interface
  • Bio Diesel Blends – Bio Diesel can degrade at a faster rate than standard Diesel Fuel. Diesel Fuel may be blended with as mush as 5% Bio Diesel without the consumer’s knowledge.

Q. What are the signs of degraded Diesel Fuel? –

A. -

  • The need to constantly change fuel filters
  • Poor engine performance – reduced RPMs at full throttle
  • Clogged, inefficient fuel injectors
  • Unexpected shutdown during engine operation
  • Fuel is discolored, cloudy and/or has water present in samples
  • Corrosion on the interior surface of the tank

Q. How should fuel be analyzed for degradation and contamination?

A. – NFPA 110 – Standard on Emergency and Standby Power Systems,

A. – Laboratory testing services should always be sought from a qualified or certified petroleum laboratory.

A.8.3.8 – Special attention should be paid to sampling the bottom of the storage tank to verify that the stored fuel is clean and dry as practical and that water, sediment, or microbial growth on the tank bottom is minimized.

Q. Why did my Generator not start?

A. – Diesel Generator Failures, David Eoff, Preferred Utilities – Power Engineering magazine August 2007
When Diesel Generators fail to start, the most common culprits are:

  • Fuel contaminated by sludge, water, or asphaltines
  • Dead or weakened batteries
  • Failed engine-cooling systems

Q. Are additives helpful?

A. – Additives are helpful; but they must be added at the manufactures’
recommended interval(s). Also, simply adding them through a single access point does little to circulate the additive throughout the fuel in the tank. Unless the additive can be thoroughly mixed with the fuel, you may be just wasting your money.

More than one additive may be necessary; (1) to combat the aging process (stabilizers) and (2) to kill microbial growth (biocides). While the biocide may kill the bacteria, fungus, and algae, the cell membranes and other particulate matter from the microbial growth is still present in the tanks and settles out in the form of sediment on the bottom (near the pick-up tube). The additives do nothing to remove the sediment or to prevent sediment from clogging filters and injectors. This sediment must be physically removed during a tank cleaning or fuel polishing program.

Stabilizing agents do help with extending the life of fuel, but constant vigilance, accurate record keeping, and routine testing is necessary to ensure the integrity of your fuel. Newer refining processes and reduced amounts of allowable sulfur have resulted in fuel being more unstable than in the past. The addition of bio-diesel is also a factor in fuel degrading faster than before.