Abstract: Turbidimeter HACH2100AN and M-151 were used to investigate the turbidity of metal detergents of calcium alkylbenzene sulfonate, calcium sulfurized phenate, calcium alkyl salicylate and calcium naphthenate. It is found that the turbidity values of detergents change as the concentration of detergent increases in the samples: increasing, decreasing, and having maximum point when HACH2100AN turbidity instrument is used. The most increase of turbidity values occurs when the instrument is in open mode and the sample concentration is 20%，the turbidity measured is close to the real value. In addition, the effect of base oil types and operation temperature of samples on measured turbidity was also explored. The results show that the type of base oil has larger effect on turbidity measured, while the temperature has only little influence. The reliability of HACH2100AN testing method is verified by the colloid sizes data of metal detergent in lube oil.

Key words: scattering light turbidimeter, detergents, turbidity, concentration