Diesel Fuel Additives

Diesel Fuel Additive Basics

Due to low and uncertain fuel qualities, any engine may benefit from using a supplemental diesel fuel additive. Diesel additives are available for any engine, including vehicles equipped with emission control equipment. Additives can offer increased fuel economy in addition to prolonged fuel system life. Further benefits may include increased cetane levels, fuel system cleaning, anti gel formulas for cold climates, and fuel stabilizers for extended storage periods. It's never to late to start using a fuel additive and there are a variety of cost-effective products readily available. Popular examples include Opti-Lube XPD, Power Service Diesel Kleen and Cetane Booster, and Archoil AR6200 Fuel Treatment Complex.


Ultra Low Sulfur Diesel (ULSD) was federally mandated by the EPA for 2007 and newer emissions regulated trucks. Since 2010, all on-highway diesel available in the United States has been ULSD. Low sulfur diesel (LSD) was the previous diesel fuel standard, introduced in the mid-90s to reduce emissions in diesel powered vehicles. LSD is classified as diesel fuel with a sulfur content of no more than 500 ppm (parts per million), while ULSD drastically reduced the sulfur content to a maximum 15 ppm. Sulfur, though not a lubricant in its elemental state, combines with other naturally occurring minerals to form a lubricant in diesel fuel.

Sulfur acts as a lubricant in diesel fuel in the same fashion as tetraethyl lead in leaded gasolines. Therefore, the transition to ULSD significantly reduced the lubricating characteristics of diesel fuel. While modern diesels were designed with the intention of burning ULSD, older engines were not. This can often result in premature wear of mechanical fuel injectors and injection pumps. While ULSD lacks in lubrication, it burns with significantly lower particulate and nitrous oxide emissions. As a result of the refining process, ULSD also has a lower energy content than LSD.

Diesel Cetane Level

The cetane level of diesel fuel represents the fuel quality in much the same fashion that octane corresponds to gasoline. Premium diesels, which are not often readily available, have a higher cetane level. Cetane level does not correspond to the grade of diesel fuel; #2 diesel is produced at various cetane levels, for example. The EPA mandates that diesel fuel sold in the U.S. must have a minimum cetane level of 40, which is often lower than what engine manufacturers specify for their products.

Cetane level refers to the amount of ignition delay when diesel fuel is injected into hot compressed air in the combustion chamber. A higher cetane fuel has less ignition delay, meaning it auto ignites faster when it is injected. Because of this phenomenon, burning fuel with higher cetane levels maximizes performance and efficiency. The actual cetane level of diesel fuel sold can vary considerably. It is commonly accepted that the benefits of a higher cetane fuel plateaus at 55, meaning raising the cetane beyond this limit yields no additional benefits.

Diesel Fuel Additives

The effects and characteristics of diesel fuel additives vary considerably by product and the market is flooded with choices. Most diesel fuel additives advertise at least some combination of the following:

Added lubricity - Supplementing the lower lubricating value of ULSD by distributing lubricating compounds into the diesel fuel. The result is often increased longevity of fuel system components, including fuel injectors and injection pumps.

Raised cetane level - Increasing the cetane level for increased performance and fuel efficiency. Performance gains are not necessarily measurable, however it has been proven that an additive can increase fuel economy by several MPG.

Fuel system cleaning - Many additives use some form of a detergent as a fuel system cleaner. While the effectiveness and/or benefit of this is not necessarily tangible, many additives do remove deposits within the fuel system. This is evident by fuel filter clogging after starting to use certain additives; always change your fuel filters after beginning to use an additive. Once the fuel system is "cleaned", you can return to your regularly scheduled fuel system service intervals.

Fuel system stabilizer - Fuel system stabilizers generally reduce or prevent sludging, algae growth, and other forms of fuel contamination (including water) while fuel is stored for extended periods.

Anti-gel formulas - Many fuel additives act as or double as an anti coagulant. Diesel fuel can gel in extremely cold temperatures, at which point it does not flow properly and an engine will not run.

A diesel fuel additive can provide any combination of these benefits. The effectiveness of individual products will vary considerably. Our best advice is to experiment with popular products until you find the balance of cost and effective results that meets your individual needs.

2 Stroke Oil & ATF as Diesel Fuel Additives

Using automatic transmission fluid (ATF) as a supplemental fuel additive is a long outdated practice. Modern ATF is packed full of additives, chemicals, and compounds that may damage fuel systems. Additionally, ATF is designed NOT to burn and will produce ash as it is combusted. This is especially dangerous to use in modern emissions regulated diesels.

2 stroke oil, although also a practice of yesteryears, has demonstrated favorable results when used to supplement the lack of lubrication in ULSD. The effects on emission controlled vehicles is not well documented and use is ill advised considering the vast availability of emissions safe fuel additives on the market.

Recommended Additives

People often ask us what is the "best" fuel additive on the market. We can't attest to the best on the market, but we have tried quite a variety of additives and these are our favorites:

Opti-Lube XPD Diesel Fuel Additive - Rated as the top diesel fuel additive in at least one renowned independent study in terms of lubrication characteristics. Also increases cetane level and helps to prevent fuel from gelling in cold weather. More expensive than many alternative products, but the numbers don't lie and this additive significantly increases the lubricity of ULSD. Entirely compatible with any diesel engine, including those equipped with modern exhaust aftertreatment systems.

At time of publishing, the price was $66.85 per 1 gallon container (price of product + shipping), which treats 512 gallons of diesel at a cost of $0.13 per gallon.

Power Service Diesel Kleen and Cetane Booster - This is our go to additive; anything and everything with a mechanical injection pump receives a dose of Power Service Diesel Kleen at every fill-up. We have not been able to perform extensive fuel economy tests but the manufacturer suggests up to 8% improved fuel economy. Completely compatible with any diesel engine, even DPF/SCR emissions systems. Readily available at most auto parts stores.

At time of publishing, the price was $27.13 per 80 oz bottle (price of product + shipping), which treats 250 gallons of diesel at a cost of less than $0.11 per gallon.

Archoil AR6200 Fuel Treatment Complex - While Archoil's most popular product is their AR9100 friction modifier oil treatment, which has been hailed as a cure-all for 7.3L and (especially) 6.0L Power Stroke injector problems, the company also produces a fuel additive. The additive seems to work just as well if you're looking for improved fuel economy; our tests showed a noticeable and cost-effective improvement with no negative side effects.

At time of publishing, the price was $44.95 per 8 oz bottle (price of product + shipping), which treats 640 gallons of diesel at a cost of $0.07 per gallon.