Can diesel fuel go bad over time? – Jalopnik

Yes, diesel can spoil over time, just like gasoline if left in your car for too long. Normally the shelf life is somewhere between six and twelve months, which is twice as long as the usual amount of unleaded gasoline. However, diesel can last longer (up to 24 months) if stored properly. When it comes to storage, national standards recommend that diesel fuel should be consumed or replaced within two years. But consider this more of a guideline, as the time period may vary depending on storage conditions and the condition of the fuel itself. Instead of relying on the calendar, look at more reliable indicators such as the smell, water content, texture and color of the fuel.

Excess water in diesel fuel can cause it to turn milky, shortening its lifespan and potentially damaging your vehicle’s internal components. Although most modern diesel engines have built-in filters with water separators, finding moisture in diesel tanks is more common than you think. Typically, diesel fuel is clear or pale yellow in color, but it is not uncommon to see red, blue, or yellow-green hues. This is not always a sign of infection; diesels mixed with red and blue dyes indicate their tax-exempt status. Government vehicles typically use blue, while red diesel is used for off-road applications such as agriculture, mining and construction. However, if your diesel fuel looks cloudy or has a dark brown color, it is most likely contaminated.

Diesel fuel can give off a foul, rancid odor when it becomes old. You will also notice a change in texture, with dirty diesel feeling thicker and more viscous. Other factors – such as hydrolysis, microbial growth and oxidation – also contribute to stored diesel going bad.

Diesel is hygroscopic, meaning it is more likely to attract water molecules. While a little water is not a problem, too much water can cause problems regardless of whether it is a diesel or gasoline engine. Water is a breeding ground for bacteria, and today’s low-sulfur diesels (including biodiesel blends) are less resistant to microbial growth, leading to the formation of diesel algae – which you might also call the diesel bug. Contaminated diesel fuel can cause all kinds of problems, including corroded fuel lines, damaged injectors and clogged filters.

Oxidation is another threat that causes diesel to spoil over time. Prolonged exposure to the air while in a storage tank oxidizes the diesel fuel, creating sludge and affecting its consistency. Chemical breakdown can also occur when diesel fuel is continuously exposed to sunlight or heat before it needs to be burned. If you store diesel fuel, be sure to keep the tank in a cool, dry place, preferably between 70 and 85 degrees Fahrenheit.

Other storage tips include using additives to extend the shelf life of the diesel. These help slow down the oxidation process and prevent microbial growth. Biocides are worth considering because they can help control bacteria in water-contaminated fuel. Use airtight tanks made of steel or high-density polyethylene to prevent moisture build-up, and fill them to reduce the air gap. Last but not least, be sure to keep the tanks clean, double check that they are dry before refilling them, and inspect them regularly for rust and water ingress.