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It’s an age-old question for diesel pickup drivers and anyone with a diesel-fueled vehicle. ‘Does diesel fuel go bad?’ In reality, there is no expiration date on diesel per se, but the performance of your diesel fuel is affected the longer you store it.

Dark and contaminated diesel fuel discarded on a white tub, captioned “Does Diesel Fuel Go Bad?”

In fact, storing diesel without properly treating it can lead to all kinds of issues, not only for the fuelitself, but for any vehicle you decide to put the fuel in later. Below, we’ll explain exactly what happens to untreated diesel fuel when stored for a long time and then talk about how you can stop these negative effects simply by treating the stored diesel beforehand.

What Happens to Diesel Fuel Over Time?

The performance of diesel fuel is significantly affected the longer it is stored. Once the fuel hits the last steps of this process, this is what we consider to be diesel fuel gone bad. If you see these things happening to your stored diesel fuel, it may already be too late to salvage it. But there are ways to elongate its lifespan which we’ll discuss below.

  • Being exposed to environmental variables creates chain reactions: The most common environmental variables that adversely affect diesel fuel are light, water, and heat. If the diesel fuel is stored in a place where it can be affected by any of these things, the molecules in the diesel fuel will create chain reactions that will lead to the fuel slowly but surely becoming less like an oil and more like a varnish.
  • The fuel darkens and gums becoming stratified: As the chain reactions occur between the environmental variables and the diesel fuel’s molecules, the diesel fuel slowly becomes thicker and darker turning into more of a gum or sludge.

This process changes the molecular structure of the diesel fuel and, with most modern diesel fuels not having the same amount of sulfur as diesel options in the past, microbes begin to grow in the fuel, creating biomass formations as well. This can produce acids which break down the fuel entirely over time.

  • The sludgy fuel won’t burn properly causing black smoke: This thicker, darker diesel fuel will not run as smoothly as a diesel fuel that is unaffected by environmental elements and will lead to black smoke and engine sputtering which is never a good thing for your vehicle.
  • The lubricity of the diesel leads to internal vehicle damage: Now that this diesel fuel no longer has the lubricity it once had, the acidic nature and thickness of the fuel will begin to adversely affect the fuel pump, diesel injectors, and engine and may not even be able to start your engine if bad enough.

How can you Elongate its High-Performance Lifespan?

Now that you know what it means when you hear that diesel fuel has gone bad, you may be wondering if there is any solution that will allow you to store diesel fuel without having it become a sludgy mess.

The answer to this is far simpler than you may have previously thought. By using a diesel fuel stabilizer, you can ensure that your stored diesel fuel is safe during all seasons. Although there are many brands and formulas out there to choose from, we recommend Opti-Lube as it is the #1 rated additive in the world and more than doubles the shelf-life of diesel fuel.

With all of this said, diesel fuel may not have a set expiration date, but the performance of stored fuel can be affected over time without proper storage and additives. If you plan on storing fuel or not driving your pickup during the winter season, it is best to choose a trusted additive like Opti-Lube and take preventative measures before it is too late.

At Gem State Diesel, we know what gummed-up diesel fuel can do to a vehicle and that’s why we chose to share this information and let you in on some of the ways we keep our fuel performing at its best no matter what. After all, it’s better to be safe than sorry, especially when it comes to something as valuable and awesome as a diesel engine.