Soot
Method: Unsubtracted JOAP (Joint Oil Analysis Program)
Units: None

Engines

Soot is a by-product of the combustion process found in all engines. Soot is an insoluble particulate that can plug oil filters and deplete the dispersant additives in the oil.

Soot is determined by the % transmittance at a set wavelength in the infrared scan. As the % transmittance decreases, the soot index increases. In other words, low % transmittance (less light passed through the sample) means a greater amount of soot in the oil.

Soot is not directly equivalent to, but closely correlates with, the pentane insolubles in diesel engines.

Effects of Soot: -

• Decreases the effectiveness of the oil.
• Can lead to piston deposits.
• Heavily sooted oil cannot maintain an adequate oil film and will lead to bearing failure.

Benefits of Determining Soot: -

• Correct management of oil change period. In conjunction with wear metal analysis, the optimum oil change period can be selected.
• Can be used as a performance diagnostic tool.
• Can be an indication of load factor for monitoring costs.

Probable Causes of Soot: -

• Rack Setting.
• Fuel Nozzle Operation.
• Turbocharger Operation.
• Air Cleaner Operation.
• Crankcase Blowby.
• Timing.
• Engine Operation; i.e., rapid acceleration, lugging, excessive idling.