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In this study, the oxidation stability, soot dispersancy, antiwear performance, and friction-reducing capability of friction modifiers (FMs) were evaluated, and an SAE 5W-30 fully synthetic oil with MoDTC type FMs was developed for heavy-duty diesel engines. In several engine tests, it was confirmed that the developed oil can double the oil drain interval in comparison with API CD SAE 30, even when EGR is applied, and improves the fuel efficiency.

Increase of soot contaminated in engine oil caused by EGR system accelerates the diesel engine wear, especially in the valve train. Wear of metal is affected by many factors such as concentration and diameter of soot, oil film thickness, oil characteristics, etc. Effects of soot on metal wear were discussed from the point of view of soot concentration, and soot diameter and oil film thickness. Wear test was carried out by using four-ball wear tester. Consequently, it was made clear that wear increases proportionally to soot concentration, and relation between oil film thickness and soot diameter plays very important role in wear mechanism. Further, the surface of wear scar was observed by SEM to discuss effect of soot diameter on wear and existence of abrasive wear by soot and its occurrence conditions were suggested.