How To Keep Your Stored Diesel Fuel Fresh

100% truth? The quality of diesel does not last and it can definitely go bad over time. The average it can be stored is from 6 to 12 months. Under the best conditions, maybe it can extend longer. Generally, if you want to lengthen the life of the quality of stored diesel fuel, the following conditions must be met:

  • Diesel fuel should be clean in the first place 
  • Be kept at around 70°F
  • Be treated with biocides & stabilizers 
  • Be maintained properly in accordance with the National Fire Protection Association (NFPA) 

If these conditions are not met adequately, the following threats can creep up and degrade the quality of your stored diesel fuel quickly after 6 months:



The exposure of diesel to water will cause it to break down - known as the hydrolysis reaction. As condensation accumulates, drops of water can drip from the storage tank roof onto the diesel. It makes diesel susceptible to microbial (bacteria and fungus) growth. 

Prevent Water From Contaminating Your Stored Diesel Fuel 

Short-Term Tips

Long-Term Tips

Use biocides

Conduct weekly check on tanks

Use fuel treatments with demulsifying properties

Empty and clean tank every ten years

Top off the tank

Cover the tank

Check tank for pooled water after the rain

Invest in an underground storage tank

Microbial Growth 

Microbial growth is often the result of water interfacing with diesel fuel: microbes need water to grow. This is a problem for several reasons:  

  • Microbes produce acids that degrade diesel fuel 
  • Clog tank filters and corrode tanks
  • Restrict flow of fluid
  • Damage engines  

On a regulatory level, however, microbe growth increase is the outcome of an Environmental Protection Agency (EPA) mandate that requires less sulfur in diesel to reduce air pollutants, but less sulfur in diesel makes the fuel less stable and prone to microbial growth.  

Tips to Prevent Microbial Growth

  • Prevent water from contaminating the diesel fuel 
  • Use biocides 
  • Prevent/Eliminate biofilm (thick, sludge-like mass)



When diesel fuel leaves the refinery, it gets introduced to oxygen and produces a chemical reaction called oxidation. Immediately after this occurs, diesel degrades and reduces its lifespan. Oxidation negatively affects both diesel fuel quality and the tank storing it. 

Tips to Minimize or Avoid Damaging Effects of Oxidation

Oxidation cannot be prevented so minimizing or avoiding its harmful effects is the goal. Some suggested solutions to this problem include: 

  • Keeping the tank cool (ideally around 20°F and not go higher than 85°F).
  • Use a fuel treatment to maintain the quality of the diesel fuel by stabilizing it. 



Another consideration…

The CSA Guideline 282-09 

The guideline states that... 

“as a minimum all fuel supplied to emergency generator sets shall be clean, clear, bright and tested annually as part of your annual fuel oil inventory maintenance program. If the fuel fails the test, the tank shall be flushed to remove built-up sludge and impurities. Unfortunately, draining the fuel without cleaning the tank leaves behind a layer of microbial growth on the tank walls and bottom. Adding fresh fuel feeds the organisms that flourish their growth.”

CSA guidelines call for the diesel fuel to be full-filtered in order to remove water, scale, bacteria growth and minimize the clogging of the fuel filter. However, there is vagueness in this because the CSA testing assumes that all water and particulates can be removed through full filtration… which it cannot. The only way it can be done is to perform an independent lab analysis on your fuel to guarantee the completion of the filtration process. 

Learn more


What do we recommend? 

For preventative measures, we recommend using our 4+ Premium. For diesel fuel that is already contaminated with: 

  1. Bacterial Growth - Treat with HUM OUT and clean fuel with a fuel polisher.
  2. Water - Use a fuel polisher to remove water, then treat with 4+ Premium and Aqua Tek. 

4+ Premium

4+ Aqua Tek

Fuel enhancer for top performance and fuel mileage improvement. A comprehensive multi-purpose diesel additive that addresses critical performance issues.

4+ Premium reduces fuel consumption, extends fuel system, engine & diesel particulate filter life, prevents costly fuel pump, and injector repairs. 

Eliminates water and prevents microbial growth in petroleum hydrocarbons such as crude, oil, lubricating oil, diesel fuel and heating oil. 

*Aqua Tek is not meant to disperse large amounts of water. If you have large accumulations, contact DSG for assistance.


For more information on keeping your stored diesel fuel fresh, please visit this link. We would also love to talk to you if you need any further expert advice. Call or text us at (306) 242-7644 or email