09-28-2025, 08:05 PM
The Shift to Ultra-Low Sulfur Diesel
In response to tightening global emissions regulations, fuel producers began reducing sulfur content in diesel during the early 2000s. By 2006, ultra-low sulfur diesel (ULSD) became mandatory in many regions, containing no more than 15 parts per million (ppm) of sulfur—down from previous levels of 500 ppm or more. While this change dramatically reduced particulate emissions and enabled advanced aftertreatment systems like diesel particulate filters (DPFs), it also introduced unintended consequences for older engines and fuel systems.
Terminology Notes
Sulfur in diesel fuel historically contributed to lubricity, helping protect metal surfaces in fuel pumps and injectors. When sulfur was removed, lubricity dropped significantly. This led to increased wear in older rotary injection pumps, especially those with tight tolerances and seals formulated for high-sulfur fuel.
Mechanics began reporting throttle shaft seal failures, hardened gaskets, and premature wear in CAV and Bosch VE pumps. In Missouri, a pump shop noted a spike in seal replacements coinciding with ULSD rollout. The shop recommended lubricity additives to mitigate damage, especially for machines built before 1995.
Additive Use and Market Response
To compensate for reduced lubricity, manufacturers and operators turned to fuel additives. Products like Stanadyne Performance Formula and Kleen-Flo Diesel Lubricant became popular among fleet managers and farmers. These additives restore lubricity, clean injectors, and stabilize fuel during storage.
Typical dosage:
Biodiesel as a Natural Lubricity Enhancer
Biodiesel, derived from vegetable oils or animal fats, naturally contains high lubricity. Blends like B5 (5% biodiesel) or B20 (20%) can improve fuel system protection without synthetic additives. However, biodiesel can gel in cold weather and may degrade rubber components in older engines.
Operators in Connecticut experimented with adding two-stroke engine oil to diesel as a low-cost lubricity booster. While not officially endorsed, this method gained traction among small fleets and rural users.
OEM Recommendations and Warranty Implications
Manufacturers like John Deere began recommending branded additives to protect fuel systems. Some manuals explicitly warn against using ULSD without supplemental lubricity agents. Failure to follow these guidelines can void warranties on fuel system components.
In New York, an equipment owner switched to bulk additive purchases, reducing cost from $0.68 to $0.24 per ounce. He calculated that protecting his injection pump cost less than $1 per tank—far cheaper than a $2,000 rebuild.
Anecdote from the Field
A truck operator in South Carolina ran a Series 60 Detroit Diesel for over 1.6 million miles without fuel system failure. He transitioned from high-sulfur diesel to ULSD and then to biodiesel blends, never using additives. His experience suggests that newer engines with hardened seals and modern metallurgy may tolerate ULSD better than legacy systems.
Recommendations for Operators of Older Equipment
The transition to ultra-low sulfur diesel was a milestone in emissions control—but it came at a cost for older engines. Reduced lubricity has led to seal failures, pump wear, and increased maintenance in legacy equipment. By using additives, monitoring fuel system health, and adapting to new fuel chemistry, operators can extend engine life and avoid costly repairs. In the world of diesel, what’s missing from the fuel matters just as much as what’s in it.
In response to tightening global emissions regulations, fuel producers began reducing sulfur content in diesel during the early 2000s. By 2006, ultra-low sulfur diesel (ULSD) became mandatory in many regions, containing no more than 15 parts per million (ppm) of sulfur—down from previous levels of 500 ppm or more. While this change dramatically reduced particulate emissions and enabled advanced aftertreatment systems like diesel particulate filters (DPFs), it also introduced unintended consequences for older engines and fuel systems.
Terminology Notes
- ULSD (Ultra-Low Sulfur Diesel): Diesel fuel with ≤15 ppm sulfur, designed to reduce emissions and support modern exhaust systems.
- Lubricity: The ability of a fluid to reduce friction between surfaces; critical for fuel system components like injection pumps.
- CAV Pump: A rotary-type diesel injection pump commonly used in older equipment, sensitive to fuel lubricity.
- Throttle Shaft Seal: A rubber seal around the pump’s throttle shaft, prone to hardening and leaking when exposed to low-lubricity fuel.
Sulfur in diesel fuel historically contributed to lubricity, helping protect metal surfaces in fuel pumps and injectors. When sulfur was removed, lubricity dropped significantly. This led to increased wear in older rotary injection pumps, especially those with tight tolerances and seals formulated for high-sulfur fuel.
Mechanics began reporting throttle shaft seal failures, hardened gaskets, and premature wear in CAV and Bosch VE pumps. In Missouri, a pump shop noted a spike in seal replacements coinciding with ULSD rollout. The shop recommended lubricity additives to mitigate damage, especially for machines built before 1995.
Additive Use and Market Response
To compensate for reduced lubricity, manufacturers and operators turned to fuel additives. Products like Stanadyne Performance Formula and Kleen-Flo Diesel Lubricant became popular among fleet managers and farmers. These additives restore lubricity, clean injectors, and stabilize fuel during storage.
Typical dosage:
- Stanadyne: 1 oz per 5 gallons of diesel
- Kleen-Flo: ~2 liters per 1,000 liters of fuel
Biodiesel as a Natural Lubricity Enhancer
Biodiesel, derived from vegetable oils or animal fats, naturally contains high lubricity. Blends like B5 (5% biodiesel) or B20 (20%) can improve fuel system protection without synthetic additives. However, biodiesel can gel in cold weather and may degrade rubber components in older engines.
Operators in Connecticut experimented with adding two-stroke engine oil to diesel as a low-cost lubricity booster. While not officially endorsed, this method gained traction among small fleets and rural users.
OEM Recommendations and Warranty Implications
Manufacturers like John Deere began recommending branded additives to protect fuel systems. Some manuals explicitly warn against using ULSD without supplemental lubricity agents. Failure to follow these guidelines can void warranties on fuel system components.
In New York, an equipment owner switched to bulk additive purchases, reducing cost from $0.68 to $0.24 per ounce. He calculated that protecting his injection pump cost less than $1 per tank—far cheaper than a $2,000 rebuild.
Anecdote from the Field
A truck operator in South Carolina ran a Series 60 Detroit Diesel for over 1.6 million miles without fuel system failure. He transitioned from high-sulfur diesel to ULSD and then to biodiesel blends, never using additives. His experience suggests that newer engines with hardened seals and modern metallurgy may tolerate ULSD better than legacy systems.
Recommendations for Operators of Older Equipment
- Use lubricity additives consistently, especially in machines built before 1995
- Monitor for seal leaks around throttle shafts and injector pumps
- Consider biodiesel blends if available and compatible with your engine
- Avoid long-term storage of ULSD without stabilizers
- Consult OEM manuals for additive compatibility and dosage
The transition to ultra-low sulfur diesel was a milestone in emissions control—but it came at a cost for older engines. Reduced lubricity has led to seal failures, pump wear, and increased maintenance in legacy equipment. By using additives, monitoring fuel system health, and adapting to new fuel chemistry, operators can extend engine life and avoid costly repairs. In the world of diesel, what’s missing from the fuel matters just as much as what’s in it.
