Abstract: The analysis results of two diesel engine oils after Mack T-11 engine test show that during the Mack T-11 engine test, the soot particle size increases with increasing of the soot concentration. The poor soot dispersity leads to a significant viscosity increase of the oil and abrasive wear due to formation of larger soot particle through aggregation. The diesel engine oil needs high enough base number to neutralize the acids from the circulation of the exhaust gas in the Mack T-11 engine test with exhaust gas recirculation system.

Key words: Mack T-11 engine test, soot, dispersity, wear, TBN