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The purposes of this paper are to develop a new laboratory oxidation stability testing method and to clarify factors relative to the viscosity increase of engine oil. Polymerized products, obtained from the oil after a JASO M333-93 engine test, were found to consist mainly of carboxyl, nitrate and nitro compounds and to increase the oil viscosity. A good similarity between the JASO M333-93 test and the laboratory simulation test was found for the polymerized products. The products were obtained not by heating oil only in air but by heating oil while supplying a synthetic blowby gas consisting of fuel pyrolysis products, NO, SO2 and air. The laboratory test has also revealed that the viscosity increase depends on oil quality, organic Fe content and hydrocarbon composition in the fuel. Moreover, it has been found that blowby gas and organic Fe accelerate ZnDTP consumption and that aromatics concentration in the fuel correlates with the viscosity increase of oil.

It is widely known that pellet-typed catalysts are deactivated by phosphorus (ZnDTP) that comes from engine oils. In this paper, the poisoning of monolithic three-way catalysts and oxygen sensors by engine oils is studied. First, catalysts and oxygen sensors were poisoned on the engine bench by test oils in which the quantity of phosphorus and ash was varied. Next, performance of the catalysts and sensors alone was examined and the vehicle exhaust emission at FTP mode was measured on a chassis dynamometer. The results indicate that phosphorus in engine oils poisons the monolithic catalyst and the oxygen sensor resulting in deterioration of the vehicle NOx exhaust emission. However, Ca sulfonate and Mg sulfonate detergents act by restraining phosphorus poisoning of the catalyst and the oxygen sensor. Through analysis of the catalyst and sensor surfaces, it is concluded that phosphorus poisons the catalyst and sensor forming a dense coating.

This paper describes lubricant technology which helps to prevent intake valve deposit (IVD) formation for use with conventional gasolines without detergents, as well as the IVD evaluation method used in testing. The FED 3462 method was modified to establish a new panel coking test method, with excellent correlation with the engine stand IVD test, for the quantitative evaluation of IVD. Tests have shown that IVD increases when the volatility of base oils becomes higher due to condensation and polymerization of engine oil additives. Furthermore, viscosity index improvers, metallic detergents and ashless dispersants have considerable effect on IVD formation. Based on various experiments, the authors have established a formulation technology for engine oils to lower IVD, which they incorporated in two newly formulated SG oils with lower IVD than conventional 5W-30 SG oil.