Updated: Mar 1, 2022
How Long Does Diesel Fuel Last?
The length of time fuel will remain useable in your tank is dependent on the fuel type. Regular gasoline has a shelf life of three to six months, while diesel can last up to a year if you don't treat, it before it begins to degrade. We will discuss the treatment below.
The storage life of any fuel is dependent on the conditions. Water contamination is one of the main enemies of any diesel-fueled equipment.
Diesel fuel can contain two types of water, water in solution or free water.
Water in solution is water that is dissolved in the fuel. These very low concentrations of water are reported in parts per million (ppm). This type of water is not necessarily a problem.
Free water is a problem, but it often does not exist in standard diesel fuel in high concentrations because it is heavier than fuel, and it drops out of the fuel and settles to the tank's bottom. It exists because of condensation. So, experts recommend you keep your tank full to minimize the amount of air and condensation that happens inside. Chances are, your diesel engine also has a water separator to help prevent it from reaching critical components where it can cause damage.
While your engine may be okay, your fuel may not be. When diesel is exposed to water, it causes a hydrolysis reaction, meaning the diesel breaks down due to water exposure. When condensation accumulates, drops of water can drip from the roof of the storage tank onto the diesel. Exposure to water creates a chemical reaction that — as mentioned — breaks down the diesel and makes it susceptible to the growth of microbes (bacteria and fungus). But, Biocide kills microbes in diesel fuel.
Since diesel fuel has had most of the sulphur removed from it, it is more prone to microbial activity than it used to be. While you may keep your fuel clean and dry, not everyone in the distribution chain may be watching things as closely as you.
So, to store diesel fuel for a long time, treat it to some Diesel Biocide Additive. It is inexpensive and is just added to the tank the next time you fill up. Still, many generators used around the world have fuel that is many years old without any problems. But why take a chance?
Many generator owners keep diesel fuel in a sealed container for many years. It is not much different than motor oil kept in a jug or barrel/drum. Without water exposure, it should keep for a long time.
It is easy to find diesel fuel additives in the automotive section of a big box store, any automotive parts supplier or gas station.
Many brands also include other stabilizers and have anti-gelling properties for untreated winter fuel to prevent it from waxing up in the cold. Just be sure to follow the instructions.