ENGINE AR 4W1757 - Caterpillar

Caterpillar EnginesBasically, there are two possible causes of severe wear and internal damage during operation of a diesel engine: Abrasive wear and corrosive wear. Abrasive wear is caused by hard, sharp particles of dirt which scratch metal surfaces and rapidly cause severe damage if allowed to enter an engine. Most dealer and customer personnel understand abrasive wear, and know the importance of proper maintenance of air filters, oil filters, breathers, etc. to keep dirt out of the engine.
Corrosive wear is not so commonly understood. It has not been a problem in areas where the sulfur content of diesel fuel is controlled at low levels. However, there are some areas where fuel sulfur content is not controlled, and some fuels in these areas have a very high sulfur content. The use of these fuels can shorten engine service life to as little as one-fifth of normal. For this reason, it is very important to understand the problem of corrosive wear and the proper maintenance necessary to protect the engine from damage.
In comparison with abrasive wear, which causes direct mechanical damage, corrosive wear is the result of chemical action. During the combustion process, the sulfur in the fuel forms sulfur oxides which combine with moisture in the air to produce sulfuric and sulfurous acids. These acids chemically attack cylinder liner walls and piston rings, and can damage exhaust valve guides and engine bearings. The amount of acid produced is in direct relation to the amount of sulfur and water present during combustion. The amount of sulfur depends on the fuel sulfur content and the rate of fuel consumption, or engine load factor. The amount of water depends on the humidity, or moisture in the air, and the rate of condensation, which is highest at low engine temperatures.
The corrosive damage from these acids is more deceptive than abrasive wear. It gradually accumulates with no warning until the damage is done. The engine will run normally with no change in power or starting characteristics until the piston rings stick or the rings and liners are worn enough to cause excessive oil consumption and/or leakage of combustion gases. The corrosion quietly destroys the engine as the acid products accumulate in the oil.
The rate and extent of corrosive wear and damage depend on these factors:
1. Percent of sulfur in the fuel.2. Load factor, or amount of fuel burned in the engine.3. Engine temperature.4. Type of engine oil used.5. Oil change intervals.6. Humidity in the atmosphere.To keep the effect of these factors at a minimum, follow recommended procedures in operation and maintenance. The recommendations are:
1. Use the best fuel available, and know the percent of fuel sulfur content. In areas where the fuel sulfur specification is not available, it will be necessary to have the fuel tested for sulfur content. Refineries in many countries do not have equipment to reduce fuel sulfur content to a low level (less than 0.4%), and the sulfur content of the fuel is frequently as high as 0.8% to 1.8%.