CONTROL OF ENGINE OIL ACIDITY

Laboratory studies of used oils from field and bench engine tests were conducted to gain a better understanding of acid-base reactions in the oil medium and the relationship between oil acidity, service and copper/lead bearing corrosion. Corrosion tests of acidic used crankcase oils have demonstrated extensive oxidative degradation of the lubricant under high temperature service conditions, with formation of oil-soluble carboxylic acids that are extremely corrosive to the lead in copper/lead bearings. Potential bearing corrosion problems cannot be inferred from the total acid number (TAN) of the used lubricant, since the TAN titrimetric technique cannot distinguish between corrosive and non-corrosive acids. Not all highly overbased detergents will neutralize organic oxidation acids; criteria other than total base number (TBN) need to be considered for control of used oil acidity. Field testing supports this conclusion. A quantitative infrared spectroscopic technique was used to confirm that copper/lead bearing corrosion inhibition by overbased detergents is directly related to the extent of acid neutralization. This technique can also indicate the role of surface protection and/or acid peptization in corrosion inhibition. Limited results on neutral metal sulphonates suggest that if bearing corrosion control relies on surface protection or acid peptization, the structure of the detergent alkylate is important irrespective of the metal cation. The lack of neutralization reactions explains the simultaneous high TAN and TBN levels often obtained with used field oils, and raises doubts concerning the value of "reserve TBN."

• Supplemental Notes:
  • Published in HS-031 026 (SAE-SP-473), "Deterioration of Automotive Lubricants in Service," Warrendale, Pennsylvania, 1980, pp 23-34. Presented at SAE Fuels and Lubricants Meeting, Baltimore, 20-23 October 1980.
• Corporate Authors:

  Imperial Oil Limited

  111 St Clair Avenue West
  Toronto, ONo,   Canada 
• Authors:
  • Cartwright, S J
  • Carey, L R
• Publication Date: 1980

Media Info

• Features: References;
• Pagination: 12 p.

Subject/Index Terms

• TRT Terms: Bearings; Corrosion; Crankcases; Detergents; Engine oils; Infrared spectroscopy; Laboratory tests; Oxidation; pH value
• Subject Areas: Safety and Human Factors;

Filing Info

• Accession Number: 00369195
• Record Type: Publication
• Source Agency: National Highway Traffic Safety Administration
• Report/Paper Numbers: SAE-801366, HS-031 029
• Files: HSL, USDOT
• Created Date: Dec 30 1982 12:00AM