What Happens to Diesel When It Sits For a Long Time?

What Happens to Diesel When It Sits For a Long Time?
Fuel sits and ages for long time

Picture this: You’ve come across a stash of diesel fuel that’s been sitting unused in storage for quite some time. You might be tempted to use it without a second thought, but have you ever wondered what happens to diesel when it sits for long periods?

In today’s world, where diesel engines power a vast range of vehicles and equipment, understanding the importance of proper fuel storage and maintenance is essential.

In this article, we’ll dive into the nitty-gritty of what happens to diesel fuel when it’s left unused, the factors that contribute to its deterioration, and the preventive measures to ensure your fuel remains in top-notch condition.

So, buckle up and get ready to learn something new!

Read this related article: How to Keep Diesel Fresh (Ways to Prevent Degradation)

Factors Affecting Diesel Fuel Deterioration

One of the primary factors contributing to the deterioration of diesel fuel is exposure to oxygen. When diesel comes in contact with air, the oxidation process kicks in. During this process, the fuel reacts with oxygen, leading to the formation of sludge and sediment. These unwanted byproducts can clog your fuel system, resulting in poor engine performance and potential damage.

Another culprit behind diesel fuel degradation is water contamination. Water can enter your fuel storage through a variety of ways, such as condensation, leaks, or even direct contact with water sources. When water mixes with diesel, it creates an environment conducive to microbial growth.

Microorganisms such as bacteria and fungi thrive in the water-diesel interface, which leads to the formation of a slimy substance known as “diesel bug.” This substance can cause corrosion and damage to the fuel system components.

Temperature fluctuations also play a significant role in fuel degradation. Changes in temperature can cause fuel to expand and contract, leading to the release of dissolved gases and the acceleration of chemical reactions.

These processes can impact the stability of your fuel, causing it to break down and lose its efficiency over time.

Read this related article: Can You Use 2-Year-Old Diesel? (Risk Associated Using It)

The Chemistry of Diesel Fuel Degradation

As diesel fuel deteriorates, the hydrocarbon chains within the fuel begin to break down. This breakdown results in the formation of gums and varnishes, which can accumulate on engine parts and negatively impact combustion efficiency.

Furthermore, the breakdown process can also produce acids that can be corrosive to the fuel system components and compromise the lubricity of the fuel, leading to reduced engine performance.

Fuel additives are an essential aspect of diesel fuel chemistry. They serve various purposes, such as enhancing fuel stability, preventing oxidation, and inhibiting microbial growth.

Antioxidants, for instance, can slow down the oxidation process, extending the shelf life of diesel fuel. Biocides and anti-microbial agents, on the other hand, can help combat bacterial and fungal growth, ensuring that your fuel remains free from harmful contaminants.

Read this related article: How Long Will Diesel Fuel Last With Stabilizer?

Consequences of Using Degraded Diesel Fuel

Using degraded diesel fuel can have several adverse effects on your engine and fuel system. For starters, sludge and sediment can clog filters and injectors, restricting the flow of fuel and leading to poor combustion.

Additionally, the corrosion of fuel lines and tanks can result from the acids formed during fuel breakdown and microbial growth.

Poor engine performance is another consequence of using degraded diesel fuel. Your engine may experience reduced power output, decreased fuel efficiency, and increased emissions, which can harm the environment.

Furthermore, relying on degraded fuel can lead to increased maintenance and repair costs, as you may need to replace fuel system components more frequently and face potential downtime and loss of productivity.

Preventive Measures and Best Practices for Long-term Diesel Storage

Now that we know the pitfalls of using degraded diesel fuel, let’s discuss some preventive measures and best practices to ensure your fuel remains in excellent condition. Selecting the right storage container is crucial. When choosing a container, consider the material it’s made from, its capacity, and ventilation requirements.

Materials that are resistant to corrosion and UV damage, such as high-density polyethylene or coated steel, are ideal for long-term diesel storage. Additionally, ensure that the container is appropriately sized and adequately ventilated to prevent pressure build-up and condensation.

Regular inspection and maintenance of your stored diesel fuel are essential to prevent degradation. Monitor your fuel storage for signs of water contamination, as water ingress can lead to microbial growth and corrosion.

Regularly check for any visible signs of microbial growth, such as slime or discoloration, and take appropriate action to address these issues.

Fuel stabilizers and additives can be invaluable in preserving the quality of your diesel fuel during long-term storage. Fuel stabilizers can help extend the shelf life of diesel fuel by preventing oxidation and corrosion.

Using additives like biocides and anti-microbial agents can keep harmful microorganisms at bay and maintain the cleanliness of your fuel.

Proper fuel rotation and usage play a significant role in ensuring fuel quality. Implementing the FIFO (First In, First Out) principle ensures that the oldest fuel is used first, preventing excessive storage periods and the accumulation of degraded fuel.

Regularly rotating your fuel and avoiding prolonged storage can go a long way in maintaining its efficiency and performance.

What Happens to This Fuel as It Ages?

As diesel fuel ages, it undergoes several chemical and physical changes that can impact its quality and performance. One of the noticeable changes is the darkening of the fuel. This occurs due to the oxidation process, which leads to the formation of gums and other byproducts. The fuel’s color can shift from a clear, amber hue to a darker, cloudier appearance.

Stratification is another issue that can arise as diesel fuel ages. This occurs when the fuel separates into layers with different densities and properties.

The heavier components, such as sludge and sediment, settle at the bottom of the storage tank, while the lighter components rise to the top. This stratification can result in inconsistent fuel quality, which can negatively affect engine performance.

As diesel fuel darkens, gums, and becomes stratified, it can lead to various problems, including:

  • Clogged fuel filters and injectors: The buildup of sludge, sediment, and gums can clog the fuel filters and injectors, restricting fuel flow and leading to poor combustion and reduced engine performance.

  • Corrosion: The acids formed during the fuel aging process can corrode fuel system components, causing leaks and damage that can negatively impact engine performance.

  • Poor combustion: The stratification of fuel can result in uneven combustion, causing reduced power output, increased emissions, and decreased fuel efficiency.

Increased maintenance and repair costs: Using aged, degraded diesel fuel can lead to increased maintenance and repair costs due to the need for more frequent fuel system component replacements and potential engine damage.

To mitigate the negative effects of aged diesel fuel, it is essential to practice proper storage techniques, use fuel stabilizers and additives, regularly inspect and maintain fuel storage systems, and adhere to a fuel rotation schedule. By doing so, you can maintain the quality and efficiency of your diesel fuel, ensuring optimal engine performance and longevity.


In summary, understanding the importance of proper diesel fuel storage and maintenance cannot be overstated. The consequences of using degraded diesel fuel can be severe, ranging from poor engine performance to increased maintenance costs and potential downtime.

By following the preventive measures and best practices outlined in this article, you can ensure that your diesel fuel remains in peak condition, ready to power your engines whenever you need them.

Remember, knowledge is power. By being informed about the factors affecting diesel fuel deterioration and the chemistry behind it, you can make informed decisions on how to store and maintain your fuel.

So, the next time you come across a stash of diesel that’s been sitting idle for a while, think twice before using it. Instead, take the necessary steps to

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