Letter - Chief Executive Officer, Clark Oil Company

November 11, 1994

Mr. Paul Melnuk
Chief Executive Officer
Clark Oil Company
St. Louis, Missouri

Ref: Clark Oil Co. Gasoline Analysis

Dear Mr. Melnuk:

Today Failure Analysis Associates, Inc. (FaAA) has been retained on behalf of Clark Oil Co. to provide an independent technical analysis of the consequences of out-of-specification gasoline produced by Clark during October, 1994. Your staff has informed me that the concentration of mercatans - organic compounds with a sulfur-hydrogen addition - present in the subject gasoline was at levels two to four times the allowable limits. Specifically, the level of mercaptans may have been as much as 80 parts per million. In addition to imparting a distinctly unpleasant odor to the gasoline, mercaptans are corrosive to some metals used in fuel system. I have been informed that there have been reports of electric in-tank fuel pumps being rendered inoperative due to rapid corrosion of the copper wires attached to the motors. I have been advised that the subject gasoline with high mercaptans fails a standard test for corrosivity with respect to a copper test strip.

Clark Oil Co. has asked Failure Analysis Associates for its initial assessment of other possible effects of using a gasoline with the alleged degree of contamination in automobiles and light trucks. One possibility is that corrosion products could clog fuel filters. Another possibility is that the mercaptans might lead to corrosion of the precision components operating with very tight clearances in the fuel injectors. Additionally, mercaptans might induce stress corrosion cracking in highly stressed small high-strength components in the injectors.

The effects of gasoline at the stated levels of contamination should, however, be confined to the fuel delivery system. The limit for total sulfur in gasoline according to ASTM Standard D 439 is 1000 parts per million (ppm). The Society for Automotive Engineers reports that actual total sulfur levels range between 300 and 1000 ppm. Once the gasoline containing excess mercaptans mixes with air in the intake manifold of an engine and burns in the combustion chamber, the unique molecular structure of the mercaptan is destroyed. The expected marginal increase in sulfur oxides in the combustion products should not have a measurable impact on the performance or reliability of other components, such as internal engine components and exhaust system components.

Some sulfur compounds will enter the crankcase of an engine in combustion product blowby past the piston rings. Modern lubricating oils are compounded with additives to neutralize these sulfur compounds. Most qualify automotive lubricating oil is dual rated for both gasoline and diesel engines. Since ASTM standard D 975 for No. 2 diesel fuel allows up to 5000 ppm sulfur, the ability of the oil to neutralize the lower sulfur levels in a gasoline engine is unquestioned. In the past the engine bearings - the components most sensitive to corrosion - had been made of copper alloys. These copper bearings have largely been replaced by aluminum bearings which are inherently corrosion resistant.

Another potential concern is the catalytic converter, which can be temporarily "poisoned" by sulfur compounds in the exhaust. Twenty years of experience with catalytic converters in automobiles has shown that their performance will recover once the excess sulfur is removed. Any partial degradation in performance of catalysts should recover once acceptable fuel is reintroduced to the subject vehicle.

The consequences of the predicted effect of the assumed degree of out-of-specification gasoline, while inconvenient, are not severe. A malfunctioning fuel pump, a clogged fuel filter or a damaged fuel injector will mimic a condition of running out of gas. This is a condition to which the driver can react and guide the car to rest at the side of the road in most circumstances.

FaAA's research into this phenomenon is continuing. As new information is available, it will be presented to you and your staff expeditiously.