We have standby diesel generators that are only run a few times a year. How long can we reasonably keep the diesel stored on site before using or disposing of it?

It is accepted that there is a finite shelf life particularly after the UK has started using B5 (5% biodiesel) but I have been unable to find any guidance or papers indicating how long it is recommended to store it.

I know that it depends on how well it is stored (contaminants etc.) but any best practice guidance / documents / journal articles that anyone could point me to would be much appreciated!

  • $\begingroup$ Watch for 'bacterial' infection as well. Really. $\endgroup$ Sep 26, 2016 at 13:28
  • $\begingroup$ "diesel bug" bacterial growth is famous in the boating crowd, where occasional use and long storage hoppens : apparently, non-bio diesel may be available from some marinas or other seaport distributors, for longer life than bio-diesel mixes. $\endgroup$ Sep 30, 2016 at 21:09
  • $\begingroup$ Note that "dispose of it" and "do nothing" are not the only options. There are companies offering "fuel polishing" services where they come out and clean your fuel on site. Dunno how well those service work though. $\endgroup$ Feb 21, 2017 at 2:50
  • $\begingroup$ Maybe there are some additives which can increase the lifetime, while not impairing the usability. Try looking into that. $\endgroup$
    – WalyKu
    Feb 21, 2017 at 10:15

1 Answer 1


The internet has a range of values from 3 months to a year, depending largely on the political/economic interest of the site in question. Here's a couple quotes that you might want to follow up on:

From springboardbiodiesel,

The truth is that all fuels will degrade over time. In fact, the EPA reports that ULSD diesel has a shelf life of between 3-6 months. Biodiesel, too, has a shelf life that can vary significantly, but with the proper fuel management, biodiesel's shelf life can be extended dramatically.

The biggest factors that affect biodiesel storage life include:

Microbial contamination Chemical contamination Exposure to light Temperature Exposure to air The type of feedstock And the additives

From BellPerformance,

All fuels degrade over time. The old school diesel fuels from the fifties could be kept relatively fresh for 1-2 years. The advent of ultra low sulfur diesel cut this storage to 3-6 months. When you blend biodiesel into the mix, the figure changes again. So there's no one stock answer to the question. A fuel's storage life is going to depend on a host of factors related to storage conditions.

The influencers of storage life for both conventional diesel and biodiesel would be contamination with microbes and/or chemicals, light, storage temperature, oxygen exposure, and the type of biodiesel feedstock that the fuel was made from.

From AssociatedPetroleum,

Most fuel today is used up long before six months, and many petroleum companies do not recommend storing petroleum diesel for more than six months. The current industry recommendation is that biodiesel be used within six months, or reanalyzed after six months to ensure the fuel meets ASTM specifications (D-6751). A longer shelf life is possible depending on the fuel composition and the use of storage enhancing additives.

At the risk of getting booted off this forum, YMMV :-)


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