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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.

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.