Sulfated Ash and Total Base Number

Sulfated ash is a lubricant property measured by a laboratory test (ASTM D 874) to determine the potential for formation of metallic ash. The ash residue is related to the oil additive composition and is significant in predicting lubricants which may cause valve distress, cylinder kit scuffing, or exhaust catalyst plugging under certain operating conditions. API FA-4, CK-4 and CJ-4 approved oil cannot exceed 1.0 wt% of sulfated ash, and CI-4 PLUS approved oil cannot exceed 2.0 wt%. Total Base Number (TBN), which measures an oil alkalinity and ability to neutralize acid using a laboratory test (ASTM D 2896 or D 4739), is related to sulfated ash level and plays an important role in controlling deposits in four-cycle diesel engines. Typically a quality engine oil will have a fresh TBN over 8.0 mg KOH/g per ASTM D 2896.