LUBRICANT ADDITIVE ACTION IN COMBATING LOW TEMPERATURE WEAR IN AUTOMOTIVE ENGINES

Studies of the low temperature wear phenomenon in a laboratory gasoline engine are presented. The relationships between wear, jacket temperature and oil quality are amplified. SO₂ formed by combustion of the sulfur in the fuel and halogen acids from excess TEL scavenger are the principal causes of corrosive wear. The dependence of wear on available alkalinity and surface protection characteristics of a wide variety of lubricant additives is demonstrated. It is shown that some additives provide only alkalinity, others only surface protection and some both. The effectiveness of surface protection depends on the type of acid molecule encountered. Surface protecting barriers exclude the larger SO₂ and bromine molecules more readily than the smaller chlorine molecule. The relative importance of alkalinity and surface protection characteristics of lubricants under extended service is discussed.