What Are Diesel Fuel Additives?

A look at aftermarket products designed to improve performance and efficiency.

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A variety of diesel fuel formulations are available in the United States, and there are even seasonal variations intended to take into account the effect of temperature on diesel. What each of these fuels have in common is specific additives designed to help improve the fuel’s performance and efficiency.

Over and above the additives pre-mixed into the diesel fuel you can buy at the pump are a host of aftermarket additives you can put in your fuel tank. Here's a look at the most common types of diesel fuel additives out there, and how they can affect your driving experience.

Beating the Cold

One of the most common diesel additives in regions of the U.S. that deal with cold winter weather is anti-gel treatment. Due to the presence of paraffin in diesel fuel, the fuel has a tendency to get cloudy and eventually solidify into a gel at lower temperatures. Biodiesel also has this issue.

Although winter-specific diesel has paraffin-free, kerosene-heavy fuel mixed in to help combat this problem, many diesel owners turn to anti-gel additives that can lower the "cold filter plugging point," which is when paraffin is solid enough to clog a fuel filter.

Keeping Moisture Out

Diesel fuel attracts moisture, which is bad news not just for an engine's operation, but also introduces the potential for corrosion inside the fuel system. To assist the mechanical water separator installed on almost every diesel engine, it's possible to use additives that reduce the risk presented by moisture.

Emulsifying additives are sometimes used in gasoline engines, but are dangerous when applied to diesel engines. They mix water and diesel fuel together to combust more effectively, while demulsifiers (helpful to diesel engines) separate them from each other, improving the mechanical separator's chances of removing water from the fuel.

Improving Lubrication and Cleaning

American diesel fuel is formulated to remove as much sulfur as possible to help reduce tailpipe emissions. As a result, this can lower the amount of lubrication provided by the fuel itself. Using biodiesel fuel can also create a similar situation.

Some diesel additives combine lubrication and detergents in order to remove engine deposits, while making up for ultra-low sulfur or biodiesel's lack of lube. You might also encounter additives that claim to improve diesel fuel's cetane number at the same time as it cleans and lubricates. Cetane, which is similar to the “octane” number in gasoline, is a chemical compound used to indicate the quality of diesel by level, with a higher number indicating better combustion,efficiency, and assisting the engine starting in colder weather. Higher-cetane diesel can also reduce emissions, helping an engine run cleaner.

Stabilizing for Storage

If you are storing a diesel-powered vehicle for an extended period of time, you'll want to consider a stabilizing additive. Depending on its composition (water content, the presence of microbes, the percentage of biodiesel used), six to 12 months of storage is possible before additives are needed.

Diesel stabilizers work to curb any algae growth in the fuel, as well as prevent sludge from forming in the tank. It further helps fight against gelling when stored at low temperatures.

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Benjamin Hunting
Benjamin Hunting is a writer and podcast host who contributes to a number of newspapers, automotive magazines, and online publications. More than a decade into his career, he enjoys keeping the shiny side up during track days and always has one too many classic vehicle projects partially disassembled in his garage at any given time. Remember, if it's not leaking, it's probably empty.