Does Diesel Go Bad & How long does It lasts + Other Important F.A.Qs

Diesel is probably the only commercial alternative to gasoline. It is especially used in transportation trucks and other heavy vehicles. With so much fluctuation in the fuel prices, many users prefer to buy diesel in bulk and store it on-site. Others choose to store it in canisters for emergency use or industrial purposes. However, sometimes the fuel gets left in storage for long durations. So, one of the primary question that persists about storing diesel is whether it goes bad? Sadly, the answer is yes, diesel can definitely go bad due to contamination if left unused for a long duration.


How long does diesel last?

Technically, diesel usually can be stored up to 6 to 12 months in a temperature of 20 degrees without incurring any significant degradation. That is the general shelf life of the fuel if it kept in a clean, cool and dry. However, this duration can also change depending on the different conditions it is exposed to. Certain factors such as fuel quality, treatments used and exposure to environmental conditions play a major role in ascertaining the duration the diesel stays fit for use. Considering that diesel is a flammable fuel that goes into the engine, it is very important to ensure that it fit for use to avoid damage to the motor parts and the automobile.


Also Read:-

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Why does diesel go bad?

Diesel, like all other petroleum based fuels, is made from a mix of hydrocarbon molecules. While for a limited period of time and in a controlled environment, diesel stays unaffected and remains useable. However, in the real world, diesel can be contaminated by a variety of factors such as water, dirt and dust.

These dust particles sometimes contain metals such as copper and zinc. Prolonged contact with such metals leads to the creation of unstable compounds. These compounds eventually breakdown and cause the oxidization of the diesel.

Similarly, moisture and humidity can also make diesel prone to microbial contamination. Microbes like fungi, bacteria and yeast exist all around us and warm conditions make it ideal for such microbes to propagate. Microorganisms that damage the fuel systems are usually aerobic, which means they need oxygen to thrive on. So, for the fuel to get contaminated there needs to be a presence of water.

Water can enter the diesel in various ways but the most common way is through the condensation that occurs due to the temperature fluctuations in the environment. Due to its microscopic size, microbes can easily enter and contaminate the fuel even with a single droplet of water. These organisms then start to propagate due to the warm and humid conditions that generally persist in the fuel systems or storage containers. The microbes lead to severe oxidation of the diesel due to the breakdown of the chemical compounds and eventually spoil the diesel.

Another problem of water entering your fuel system is the increased chances of corrosion. Corrosion can further lead to issues such as increased metal contaminants in your fuel. So, the moment the fuel has metals, it is prone to further chemical reactions that may lead to the oxidization of the diesel. Further, rust or corrosion can lead to sediment formation which may clog your fuel filter and damage the motor filter. So, water in your diesel can be fatal for your favourite automobile as well as any other diesel based motor.

There has been a persistent point being raised about how in the older days diesel had a much longer shelf life, unlike the modern diesel fuels that usually doesn’t last more than a year. There are basically two primary reasons that experts have pointed out for the quicker containment of diesel in the present day –

  • Firstly, the reduction of sulphur levels by up to 97% in diesel fuels to make it more environment-friendly may be a reason for the increased chances of contamination. Sulphur acts as a deterrent for microbial growth and its reduction has allowed these microbes to grow unhindered.
  • Secondly, the increased levels of biodiesel in the diesel composition have led to an increased risk of microbial infestations. Biodiesel, which is also known as FAME (Fatty Acids Methyl Esters) biodiesel tends to absorb more water from the atmosphere and hence, make it more prone to microbial contamination.


How to identify if the diesel has gone bad?

The simplest way to check for the contamination of diesel is by comparing the old diesel with fresh diesel using two glass jars. The old diesel is likely to be more dark and thicker than fresh diesel. Diesel can turn bad due to contamination by microbes or due to reactions with metals. In both these cases, the fuel is usually oxidized due to the chemical reactions that break down its compounds. Microbes are too small for the human eye. Contamination may also be spotted in the form of a biofilm, which usually appears as a shiny film or layer that floats on top of the fuel. Another sign is the accumulation of biomass or microbial cells which looks like a thick, slimy liquid. So, these are some of the ways to identify if your diesel is contaminated.


What are the symptoms of contaminated diesel?

Contaminated diesel can be very problematic for your automobile and its best if spotted early. So, one of the first symptoms of contaminated diesel is the “check engine” light. It is one of the first things that get illuminated if there is any problem with the fuel and it is also something that most people ignore as a mini malfunction since the vehicle seems to be running just fine. However, the fact is that in most cases, the “check engine” light gets turned on when the engine are not working right and one of the possible reasons could be contaminated diesel fuel.

Another reason could be the drop in mileage since the contamination leads to the thickening of the diesel and causes a drop in the CETANE levels which prevents the diesel from burning like it ought to and making it less efficient. It can also lead to frequent clogging of the fuel filter and corrosion in the fuel tank due to the reduced lubricating ability of the diesel.

Contaminated diesel could also lead to damage in the engine parts and cause problems such as spluttering, power loss and eventually a complete breakdown of the engine due to restricted fuel flow. So, what could have probably been avoided at the cost of a few extra bucks and some caution will end up costing you thousands of dollars. Hence, it is very important to keep a watch out for such symptoms and to take immediate measures to reduce the extent of damages to your automobile.


How to extend the shelf life of diesel?

There are various steps which can help extend the shelf life of diesel. One of the first step to prevent diesel contamination is to only buy it from a reputed supplier who can ensure that it is of good quality. It is always best to ask a couple of questions about the storage facility and understand the supplier’s handling procedures. Another important step is to keep your fuel systems of your vehicle well maintained since a corroded system is likely to cause contamination of your fuel.

It is also smart to practice habits of maintaining storage hygiene when storing diesel such as sanitising storage tanks and regularly testing for containment. Some of the popular contamination tests are –

  • Colony Forming Unit (CPU) Test – CFU tests use an incubator to grow and calculate the density of microbes present in the sample. However, it is a difficult test which has to be completed within 24 hours of sample collection and takes about 4-10 days to produce the result.
  • Immunoassay Antibody Test – It is a modern test that works using the ‘add drops and wait’ system which helps deliver instant results within 15 minutes. It requires minimal equipment such as a clean sampling container and a hygienic surface.
  • ATP Test – ATP testing is another method of instant contamination detection which looks for the total microbial content in a sample. However, the main problem here is the risk of external contamination during the process of sample collection.

Lastly, you may also treat your diesel by adding fuel additives to help reduce chances of fuel contamination. Fuel additives contain chemical compounds that prevent microbial growth and also help boost fuel stability and lubrication. So, adding such fuel additives will definitely help you extend the shelf life of your diesel.


Does diesel go off in a car?

Yes, diesel can definitely go off in a car. In the absence of any other contaminants, diesel can stay good for a period of up to 6 to 12 months. However, the natural environmental factors such as climate changes such as dust, heat and humidity will eventually lead to contamination of water and other pollutants even in your car’s fuel tank. As soon as the water enters the diesel, it also brings with it polluting microbes. Over time these polluting microbes are likely to start developing and start causing the diesel to oxidize. Once oxidization starts, the fuel will start to become thick and eventually end up going bad. So, it is best to not leave your tank filled if you plan to leave your car unused for prolonged periods of time.


Does diesel go bad like gas?

Yes, diesel can definitely go bad like gas. While gasoline has a lot more volatile compounds than diesel, so, it is likely that gas will go bad sooner than diesel. However, if left untreated, diesel too can go bad due to the contamination of microbes and other pollutants and bad diesel can adversely affect your vehicle.  So, it is best to treat the diesel with the proper additives or to avoid storing it for long duration altogether.


Does diesel last longer than gas?

Yes, due to the absence of volatile compounds that are generally present in gasoline, diesel does have a longer shelf life. However, it is always smart to take the precautionary measures before using diesel that has been left out for too long.


Does diesel go bad in a jerry can?

Many people use jerry cans to store diesel for various purposes. Sometimes, it may be left in the can for longer than they had planned to. However, the sad news is it is likely that it will be unusable once it crosses its shelf life of 6 to 12 months. Moreover, a jerry can is not 100% sealed and is more prone to contamination due to factors like condensation, dirt seepage and temperature fluctuations than a properly sealed storage container. So, it is best to either avoid using the diesel or to use the relevant treatments and to test the diesel before letting it into your car’s fuel system.


Is 10 year old diesel fuel still fit for use?

No, 10 year diesel is absolutely not fit for use in your automobile. We all know that diesel has a shelf life of 6 – 12 months, so if is stored for a period of 10 years, even in a sealed container, it is most likely to become unusable. It will most definitely be affected by the natural processes such as sedimentation, algae growth and microbes and eventually degrade over the years. So, if you find diesel that is over 10 years old, it is best to not test it on your vehicle.


How long does diesel last in a boat?

It is true that boating is not for all seasons and the diesel in your boat is likely to stay unused for extended durations. However, it is important to remember that water and humidity are among of the main reasons for the degradation of your diesel and sadly, your boat constantly is surrounded by both. So, if you have left it untouched beyond the diesel’s shelf life and you don’t want to any issues to spoil your boating trip, it is best to refill your tank with fresh diesel.


What to do with old diesel?

Although old diesel can be reused or maybe even resold if left uncontaminated, it is very important to check for contamination. Contamination may cause severe damage to any machine the diesel is used in. so, if the diesel is contaminated, it is best to drain it down in a safe manner. Considering the fact that diesel can be a hazardous contaminant to the environment, it is best to either contact personnel equipped for handling such waste or to leave it at the local recycling centre for proper disposal.



Diesel under optimal conditions has a shelf life of 6 – 12 months, after which it starts to degrade. Such degradation may occur due to a range of different environmental factors. While additives may extend the life of the fuel, it still does not make it immortal. The inevitable truth is that diesel will go bad if left unused and using contaminated diesel may end up costing you much more than you planned on saving by reusing the old diesel. Thus, it is best to either run the appropriate tests on old diesel before using it or to avoid storing the fuel altogether.