CRANKSHAFT GP 3967055 - Caterpillar

The Fuel Sulfur Problem
When diesel fuel is burned in an engine's combustion chamber, the fuel sulfur is chemically converted to sulfur oxides. These compounds, in turn, react with water vapor to form sulfurous and sulfuric acids. As the vapors condense in the valve guides and in the piston ring area, the acids can chemically attack the metal surfaces and cause corrosive wear.
Neutralizing The Acids
One function of the lubricating oil is to neutralize the acids and, thus, retard the corrosive damage. Certain additives used in lubricating oils contain alkaline compounds which are formulated to neutralize these acids.
The measure of this reserve alkalinity in a lubricating oil is known as its Total Base Number or TBN. The Total Base Number is measured by one of two procedures: American Society For Testing Materials (ASTM) D-2896 or ASTM D-664. Caterpillar's recommendations are based on ASTM D-2896.
The higher the initial TBN value generally indicates more reserve alkalinity or acid-neutralizing capacity. To minimize corrosive wear caused by increased fuel sulfur levels, engine oils which have higher TBN values are essential.
The New Oil Recommendations
Caterpillar's new recommendations provide a means of combating the undesirable effects of high sulfur fuels. New guidelines have been developed for the selection of oils that permit STANDARD OIL CHANGE INTERVALS (as per the applicable Maintenance Guide) when using diesel fuels with sulfur contents of up to 1.5 percent.
Caterpillar previously based its standard oil change intervals on a fuel sulfur content of 0.4 percent and recommended shortened change intervals when fuels with greater than 0.4 percent sulfur content were used.
In the past, Caterpillar has recommended specific service classifications of oil, such as API (American Petroleum Institute) Class CD, but has not specified or published any alkalinity reserve (TBN) information. Because the range of TBN values is wide and because there is an increase in the sulfur content of some diesel fuels, it is important that TBN information be readily available. To satisfy this need, the TBN information is now included in the Engine Manufacturers Association's "Lubricating Oils Data Book For Heavy Duty Automotive and Industrial Engines." This is available from Caterpillar by Form No. SEBU5939.
The Correct TBN
The first step to determine the correct TBN value is to find the fuel sulfur content. This information should be available from the fuel supplier. If it is not, a fuel sample should be analyzed by a competent, independent laboratory.
When the sulfur content is known, use the graph shown in the illustration to determine the necessary TBN value. For fuels with sulfur content above 0.5 precent by weight, the TBN value should be 20 times the measured fuel sulfur content. The upper broken line is used to determine the necessary TBN value for new oil. New oils having the recommended TBN values will provide acceptable neutralizing performance through the standard change interval.
The lower solid line on the graph provides information needed to determine the minimum TBN value for used oil. The TBN of used oil must be established using the ASTM D-2896 procedure.
Note that the limits