Diesel Additives and Lubricity in the Age of Ultra-Low Sulfur Fuel

[MikePhua]

The Shift to Ultra-Low Sulfur Diesel and Its Consequences
Since the early 2000s, diesel fuel formulations have undergone significant changes to meet tightening emissions regulations. One of the most impactful shifts was the introduction of Ultra-Low Sulfur Diesel (ULSD), which reduced sulfur content from 500 ppm to 15 ppm. While this change dramatically lowered particulate emissions, it also stripped away much of the natural lubricity that older diesel engines relied on to protect fuel pumps and injectors.
Sulfur itself is not a lubricant, but the refining process used to remove it also eliminates other compounds that contribute to fuel system protection. As a result, operators of legacy diesel engines—especially those built before 2007—have increasingly turned to additives to restore lost lubricity and maintain performance.
Terminology Annotation

• Lubricity: The ability of a fluid to reduce friction between surfaces in relative motion. In diesel engines, it affects wear on injectors and fuel pumps.
  
• Cetane Number: A measure of diesel fuel’s ignition quality. Higher cetane improves cold starts and reduces engine knock.
  
• Detergency: The capacity of an additive to clean fuel system components and prevent deposit formation.
  
• ZDDP (Zinc Dialkyldithiophosphate): An anti-wear additive commonly used in engine oils to protect metal surfaces under high pressure.
  

Popular Additives and Their Reported Effects
Operators across North America have experimented with a wide range of diesel additives, each offering different combinations of lubricity enhancement, cetane boost, and cleaning agents. Among the most frequently mentioned are:

• Power Service Diesel Kleen: Widely available and often used for winter anti-gel protection. Mixed reviews on lubricity improvement.
  
• Opti-Lube XPD: Frequently cited in independent studies as one of the top performers in restoring lubricity. Also includes cetane enhancement.
  
• Stanadyne Performance Formula: Developed by a fuel system manufacturer, offering balanced protection and injector cleaning.
  
• Schaeffer’s Diesel Treat 2000: Known for high concentration and low treatment cost per gallon. Users report cleaner EGR valves and improved fuel economy.
  
• Howes Diesel Treat: Popular in colder climates for its anti-gel properties, with moderate lubricity support.
  
• Lucas Fuel Treatment: Common in retail outlets, praised for simplicity but criticized for lack of data-backed performance.
  

Some operators also use unconventional additives:

• Two-stroke oil: Added for lubricity, especially in older engines. Typically mixed at 1:200 ratio.
  
• ATF (Automatic Transmission Fluid): Once popular as a fuel system cleaner, now discouraged due to ash content and regulatory concerns.
  
• Canola oil: Used experimentally for lubricity and cleaning. Its high flash point and natural detergency make it effective, but filter clogging is a risk during initial use.
  

Field Experience and Anecdotes
In Canada, a trade school conducted tests using canola oil and biodiesel blends. They found that 5% biodiesel restored lubricity to safe levels and cleaned fuel systems effectively. However, filters clogged after the first few tanks due to carbon removal. After flushing, performance stabilized and emissions dropped noticeably.
In Texas, a mechanic noted that Schaeffer’s additive was the only one that prevented EGR valve buildup in a fleet of trucks. He reduced cleaning intervals from every 20,000 miles to over 60,000 miles, saving labor and downtime.
In Michigan, a farmer reported that Power Service failed to prevent injector wear in his older tractors, while switching to Stanadyne eliminated hard starts and improved throttle response.
Recommendations for Additive Use
To select and use diesel additives effectively:

• Match the additive to your engine’s age and fuel system type. Older mechanical injection systems benefit most from lubricity enhancers.
  
• Use additives that meet ASTM D975 standards and are compatible with ULSD.
  
• Monitor fuel economy and engine behavior after switching additives.
  
• Change fuel filters after initial use of strong detergents or bio-based additives.
  
• Avoid additives with high ash content in engines equipped with DPFs or EGR systems.
  

For legacy engines, consider additives with:

• Lubricity agents (e.g., esters, fatty acids)
  
• Cetane boosters (e.g., nitrates)
  
• Detergents (e.g., polyetheramines)
  
• Corrosion inhibitors
  

Industry Trends and Regulatory Impact
As emissions regulations continue to evolve, fuel formulations will likely become even cleaner—and potentially drier. Additive manufacturers are responding with multi-function blends that address lubricity, emissions, and fuel stability. Some OEMs now recommend specific additives for warranty compliance, especially in high-pressure common rail systems.
Meanwhile, the rise of renewable diesel and synthetic fuels introduces new variables. These fuels often have excellent combustion properties but may lack lubricity unless treated. Operators should consult engine manufacturers before switching to alternative fuels.
Conclusion
Diesel additives have become essential tools for maintaining engine health in the ULSD era. While no single product suits every application, understanding the roles of lubricity, cetane, and detergency helps operators make informed choices. Field experience, independent testing, and careful observation remain the best guides in selecting the right additive for your fleet. Whether using commercial blends or experimenting with bio-based solutions, the goal remains the same: protect the engine, improve performance, and reduce long-term costs.