How Long Does Diesel Fuel Last In Storage?

One of the costs that has to be factored in when dealing with any sort of transportation work is fuel. The large fluctuations in diesel fuel prices – especially in recent times – many choose to buy in bulk, storing the fuel they need for their trucks on-site, yet even this has a cost attached to it. There are costs associated with leaving fuel unused, but more importantly, there are the issues of fuel degradation.

How Long Does Diesel Fuel Last?

The problem here is twofold. First, diesel fuel is carbon-based petrochemical and thus starts the process of oxidization as soon as it departs the refinery, with the sediments and gums that clog fuel beginning to form. So how long does diesel fuel last? Well, without diesel fuel additives, diesel can go bad in as little as 30 days before this oxidization process becomes unwieldy, creating deposits that can damage fuel injectors, fuel lines, and other system components which will hurt fuel economy and performance.

Water is a major issue in diesel fuel for a couple of reasons. One is new blends of diesel often contain some biodiesel which inherently has more water in it. This water, if not separated from the fuel, can make it through the system and into the fuel injectors.  Newer common rail fuel systems run at pressures up to (40,000) PSI. If even a tiny droplet of water makes it through one of the new high-pressure systems to the fuel injector it can blow the tip-off, which is an expensive repair. Just like oxidization, this slime will clog the fuel and impart long-term damage.

You can minimize your water issue by keeping your tank full which minimizes the amount of condensation space in the tank, thus reducing the amount of water. Secondly, you can use diesel fuel treatments which demulsify or separate water from the fuel. Almost all diesel engines are equipped with a Fuel Water Separator (FWS) filter. Demulsification enhances the performance of the (FWS).  All OEM manufacturers recommend that you demulsify water from diesel fuel so it can safely be removed and not damage your engine. Standard good fuel maintenance practices need to be followed for fuel storage tanks. Those practices involve periodic removal of water that has gathered at the bottom of the tank. Water is heavier than fuel and free water will drop to the bottom which is a better place for it than in your fuel system. Maintenance doses of a dual phased (works in water and fuel phases) biocide twice a year are also recommended to prevent microbial growth.

For oxidization, you’ll want to invest in a diesel fuel stabilizer; Diesel fuel is very different from gasoline and needs specific technology to work properly. For best performance do not use fuel additives that claim to work in both gas and diesel. 

Fuel stabilizers called antioxidants are necessary for any storage longer than 30 days and should be used while the fuel is still fresh. While it’s necessary for diesel storage, it’s wise to use it in any vehicle that hasn’t been used with some frequency. 

What Does the Fuel Industry Say? 

So how long does diesel fuel last under these conditions? Exxon states that “diesel fuel can be stored 6 months to 1 year without significant fuel degradation if you keep it clean, cool and dry.” Chevron adds that diesel fuel can be stored longer than a year under certain conditions:

• First, the fuel was purchased clean and dry from a reliable supplier.
• Second, appropriate fuel quality and stability was achieved through the use of additives, including biocides, stabilizers and additives packages that increase lubricity, improve the Cetane number and provide detergents for keeping fuel systems clean.
• And lastly, the fuel was regularly tested, maintained and, as necessary, polished through portable filters.

So, the answer to “how long does diesel fuel last” is “it varies.” But with proper fuel stability gained through sound storage and the use of diesel fuel treatments like Diesel STA-BIL® you can fight off fuel degradation for a relatively long period of time and keep costs low and controlled.