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The relationship between engine oil formulations and catalyst performance was investigated by comparatively testing five engine oils. In addition to one baseline production oil with a calcium plus magnesium detergent system, the remaining four oils were specifically formulated with different additive combinations including: one worst case with no detergent and production level zinc dialkyldithiophosphate (ZDTP), one with calcium-only detergent and two best cases with zero phosphorus. Emissions performance, phosphorus loss from the engine oil, phosphorus-capture on the catalyst and engine wear were evaluated after accumulating 100,000 miles of taxi service in twenty vehicles. The intent of this comparative study was to identify relative trends.

The low-temperature pumpability of engine oil throughout the engine at startup is an important property. Insuring that fresh oils can be pumped at low temperatures has been a requirement of crankcase lubricants for approximately two decades. Extending the assurance of the oil's low temperature pumpability as it ages under engine operation has been the concern of car manufacturers and lubricant marketers for some time. In order to determine the factors influencing the aged oil's low temperature pumpability, we have undertaken a fleet test. We found that as lubricants are aged, excellent low temperature pumping properties can be maintained if lubricants are formulated with viscosity-index improvers incapable of forming polymer networks, base oils with a low tendency to form wax networks, effective pour-point depressants, and if oil drain intervals are not extended beyond the performance limitations of the specific lubricant category.

Oils, which do not contain Molybdenum (Mo)-based friction modifiers, were aged in vehicle and engine fuel economy tests in order to determine if the different aging protocols caused similar changes in the physical and chemical properties of these oils. Vehicle and engine tests were found to cause similar changes in the high temperature high shear (HTHS) viscosities and boundary friction coefficients of oils. We also observed that the extent of oil oxidation, nitration and volatilization occurring in the vehicle tests could be duplicated by aging in the engine tests. The fuel economy performance of aged oils was also measured in engine tests and found to be highly dependent upon the aged oil's HTHS viscosity. However, we observed that an aged oil's boundary friction coefficient, by itself, did not correlate to an aged oil's fuel economy performance in the high temperature fuel economy measurement stages of engine tests.

The effect of critical physical properties of engine oils on fuel economy performance in General Motors (GM) vehicles has been measured. Reductions in an oil's high temperature high shear viscosity, boundary friction coefficient and pressure-viscosity coefficient were found to equally improve fuel economy. These same oil properties affect fuel economy measured in the Sequence VIA engine test. However, fuel economy performance in GM vehicles is more dependent on an oil's boundary friction coefficient and pressure-viscosity coefficient than that measured in the Sequence VIA engine test. New fuel economy measurement conditions have been proposed for the Sequence VIB engine test. Changes in an oil's boundary friction coefficient were found to have the same effect on fuel economy measured under these new measurement conditions as that measured in GM vehicles.

A 100,000-mile fleet test in nine gasoline-powered passenger cars was carried out. The impact of motor oil phosphorus levels on engine durability, oil degradation, and exhaust emissions has been previously described. The results of additional emissions control systems studies, and measurements of the engine oil additive elements which are present on the catalysts, are now presented. These studies include conversion efficiencies for the aged catalyst at the end of the test by a combination of light-off experiments, air/fuel sweep tests, and an auto-driver FTP. The performance of the lambda sensors is also presented. The relationships between engine oil additive levels and composition and emissions systems durability is presented.

A 100,000-mile fleet test was carried out on nine 1991 gasoline-powered passenger cars employing an API SH/CD motor oil and two reduced phosphorus analogues. The lower-phosphorus oils have zinc dialkyldithiophosphate (ZDDP) treat rates that fall below the proposed ILSAC GF-2 maximum phosphorus limit (0.11%). Gaseous tail pipe emissions were measured at various intervals according to the EPA FTP City Emissions Test 75 driving cycle. A good correlation between phosphorus level and emissions degradation was obtained when starting emissions levels and oil consumption was accounted for in the analysis. Few differences were observed between the highest-phosphorus oil (0.11%) and the lower-phosphorus (0.08% and 0.06%) oils in the typical end of test engine cleanliness parameters. There were no significant differences in either valve train or cylinder wear between the oils. The used oils had similar analytical inspections.

Varying amounts of many kinds of chemical agents are used in both gasoline and diesel engine oils to provide the performance characteristics required by modern engines. These additives adapt the oils to changing temperatures, reduce friction, prevent wear and alleviate the many problems caused by combustion-chamber blowby in the crankcase and the area of the piston rings.