Fuel - Low Sulfur Diesel

REF. NO. MBNA 00/55

TO: OUR MERCEDES-BENZ PASSENGER CAR DEALERS

DATE: June 1994

SUBJECT:
LOW-SULFUR DIESEL FUELS

As of the fall of 1993, newly formulated diesel fuels were introduced to meet Federal (low sulfur) and California (low aromatics) emission requirements. It should be noted that low sulfur diesel fuels have already been used in Southern California since 1985.

Mercedes-Benz supports the introduction of these environmentally friendly fuels, i.e. fuels with low sulfur content and reduced aromatics. In order to assure trouble-free operation of our products, the new fuels must have similar characteristics when compared to current fuels. Lubricating characteristics and reaction of gasket materials are areas that could be especially affected by these new fuels.

Fuel pump lubrication

Experience and endurance tests have shown that the use of these new fuels with In-line fuel Injection pumps common to our diesel engines have not caused any wear problems, since these pumps are lubricated with engine oil and, therefore, are not dependent on diesel fuel for lubrication.

Fuel leaks

In most cases, reports of leaks in Mercedes-Benz diesel engines have been associated with aged injector element O-rings. The age of a seal can be represented by a number of factors, i.e. mileage, age and hours of use. Other factors can also influence the aging of seals/hoses, including maximum temperature, number of thermal cycles, and exposure to oxidants. However, in a recent analysis, mileage was the most widely available indicator of seal age.

In vehicles operated for an extended period of time on the prior diesel fuel and then switched to low-sulfur/low aromatic diesel fuel, this process can be accelerated dub to reduced swelling or shrinkage of O-rings, primarily caused by increased fuel oxidation.
Low sulfur and/or low aromatic levels in diesel fuels may not be directly causing the reported problems. Rather, according to recent reports, the manufacturing process by which the lower sulfur and lower aromatics levels are achieved may be causing the problems. This process is known as hydrotreating. The effect of hydrotreated fuels on swell/shrinkage characteristics of nitrite rubber components as well as the effect of increased oxidation with potential damage to seals is being further investigated by the fuel manufacturers.

Replacement of aged seals will solve seepage problems.

New vehicles

Vehicles operated from the start with the new diesel fuels should not be affected by the low sulfur/low aromatic diesel fuel. In fact, this fuel offers higher beneficial factors such as higher cetane rating and lesser propensity to contaminate engine oil.

Aftermarket Additives

Mercedes-Benz has never recommended the use of aftermarket fuel additives. Currently, there are no known additives which are effective on leaks.