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Beware of the new ULSD also known as S15!
Date Line 2 June 2006

    The transition to S15 also known as ULSD or ultra low Sulphur diesel fuel has occurred on Oct 15th, 2006 here in the United States. S15 has only 15 parts per million of sulfur compared with the previous S500 which has 500 parts per million. Sulfur is a lubricant in the diesel fuel delivery system. The process to remove the sulfur also removes the aromatic hydrocarbons which is the chemical that keeps diesel fuel system seals plump & pliable. This new S15 diesel fuel will enable advanced exhaust after treatment technologies in 2007 & newer diesel engines, such as catalytic particulate filters. The EPA and the DTF are both calling it a clean diesel milestone. While owners of 2006 & older diesel engines are all about to call it a diesel engine disaster.

Facts: Sulphur is a diesel engine lubricant. Prior to the early 1990's Sulphur content of diesel fuel was 5000 PPM. In the early 1990's the EPA mandated a cut of Sulphur to 1/10 the previous levels & S500 or 500 PPM Sulphur content fuel was born. This low Sulphur fuel caused a huge problem with diesel fuel system injection pumps burning out because of loss of the lubricating Sulphur. Fast forward to Oct. 15th 2006 & the EPA did it again by requiring no more than 1/33 the previous Sulphur content. Now we have S15 or 15 PPM Sulphur content in our diesel fuel. What is more, because of the technology required to wash out the Sulphur in the fuel the side effect is it also washes out the aromatic hydrocarbons that keep fuel system seals pliable.

The Problem: Chevron states that the new ULSD (15 PPM Sulphur) EPA fuel mandated for October 15, 2006 at your favorite diesel station fuel pump may cause your IP pump seals and other fuel system o-rings to fail because of the lack of aromatics in the newly mandated diesel fuel will cause the seals to shrink. Chevron says you are responsible for repair costs as the EPA has mandated this new diesel fuel.

Our Solution: While we admit that BioDiesel contains fewer aromatic hydrocarbons: benzofluoranthene: 56% reduction; Benzopyrenes: 71% reduction, compared with #2 diesel fuel, it still contains more aromatics than the new ULSD being discussed. The addition of a small amount of BioDiesel, may help and BioDiesel is known to be a great lubricant. It is also known to contain aromatics which swell older types of o-rings. So, our recommendation is to add at least some (depends on how much you are comfortable adding) BioDiesel to your diesel tank at every fill up to keep those seals nice & plump! See manufacturers BioDiesel recommendations here

Don't take our word for it....
Read what Chevron says about pending seal failures

Technical Bulletin Chevron Products Company
    Some vehicle owners, who recently began using the new EPA regulated ultra low sulfur (S15) diesel fuel, report that their vehicles have developed fuel leaks. Similar occurrences were reported in the early 1990’s when low sulfur fuel (S500) was introduced. The leaks in the 1990’s occurred at points where elastomers (O-rings) are used to seal joints in the fuel system.  During the 1993-94 period, the most common occurrences were injector fuel pump leaks.
    This problem is not exclusive to one engine type, one fuel type, or one geographic region. It can affect some engines that are older than ten years, but some newer ones have experienced the problem as well. 
    The reoccurrence of these fuel leaks could become widespread geographically when the majority of fuel supplies are switched to S15. However, it is anticipated that only a very small fraction of the vehicles may be affected. Of course it can be serious for owners whose vehicles are affected.
    Chevron is working with diesel equipment manufacturers and providing technical support to fleets. The evidence to date suggests the problem is linked to a change in the aromatics content of the S15 ultra low sulfur diesel fuel, to seal material and age of the material.


    In October 1993, the 1990 Clean Air Act Amendments required that diesel fuel for “on highway” vehicles contain no more than 0.05 percent sulfur by weight. Before this, diesel fuel typically contained 0.2 to 0.4 percent sulfur by weight. Reports of fuel system seal leaks surfaced shortly after the introduction of the then new fuel designated as S500. Affected components were mostly fuel pump and injectors. Starting June 2006, refineries will be required to produce diesel fuel with a  much lower sulfur level (15 ppm) than was contained in S500 (500 ppm).  The new fuel is commonly known as ultra low sulfur fuel designated as S15 by the ASTM standard D 975. As noted earlier in some areas where this new S15 fuel has been introduced ahead of schedule, some occurrences of similar fuel leaks have been reported.
    Should further elastomer failures occur, they are expected to be sporadic.  Seals in some vehicles may fail while similar seals in other vehicles using the same fuel may not.  Past experience indicates that the common denominator is expected to be nitrile rubber (Buna N) seals that have seen long service at high temperatures. High temperatures have a tendency to accelerate seal aging. The reduction in sulfur content is not responsible for the problem.
Two explanations have been offered to explain the sudden occurrence of seal failures:
Many of the new S15 fuels are expected to contain lower levels of aromatics.  The change from a higher to a lower aromatics fuel can cause seals to shrink.
    Aged seals, which do not have the elasticity to adapt to this change, appear to fail sooner.
    Some of the new S15 fuels are expected to be more susceptible to oxidation. The resulting oxidation products (peroxides) could attack the seal material and cause it to prematurely age.
To date we have not seen evidence of peroxide formation, therefore, we believe that most cases are related directly to the reduction in the aromatics content of the fuel. This reduction is a result of increased hydrotreating to reduce fuel’s sulfur level to 15 ppm. Fuel additives do not appear to be a solution, since they do not change the aromatics content of the fuel. The seal failure is not related to fuel lubricity. Lubricity affects wear of metal parts.  There is no relationship between the fuel lubricity level and the elastomer failure. Currently all fuels in the U.S. must meet a minimum lubricity level. The elastomer failures in the 1990’s were addressed by a California Governor’s Task Force. A comprehensive report was issued in 1994 which includes more details about this subject. For an online copy go to: 9.pdf
    If you have a diesel fuel system that is leaking, Chevron recommends that you contact your equipment manufacturer for advice on the choice of a replacement elastomer for the seals and future maintenance schedule.  Newly replaced seals should not develop a leak.

If you have not experienced this problem, you still may wish to consult your equipment manufacturer about a maintenance schedule for your aged nitrile rubber (Buna N) seals and manufacturer’s experience with lower aromatics diesel

Chevron Products Company FTB-2-1 August/2005



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