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Lengthening the engine oil-change interval would reduce the frequency of automotive maintenance, reduce the amount of oil required to service the car population, and reduce the potential pollution problem resulting from the disposal of the used oil. Tests were run using 1967-1972 model U.S. passenger cars, operating in several types of service. Using unleaded instead of leaded gasoline reduced deposits and wear. With unleaded gasoline, doubling the oil-change interval had no significant effect on deposits and wear, but did increase oil filter plugging frequency. Deposits and wear were less with unleaded gasoline and doubled oil-change interval than with leaded gasoline and “standard” oil-change interval. Doubling the concentration of additives used in current quality oils was more effective at reducing deposits and wear than was doubling the engine crankcase ventilation rate.

The recent increase in excessive camshaft and lifter wear after extended service has shown that some SE-quality engine oils do not provide adequate protection. To determine the effects of oil additives on wear, controlled tests were run using 1972-1974 model cars, unleaded gasoline, and either SE commercial products or experimental formulations. Field experience with 1970-1975 model trucks, leaded gasoline, and SE/CC or SE/CD oils was also investigated. With some commercial oils, in both controlled tests and field experience, excessive wear sometimes occurred after extended service, even with recommended oil-change intervals. Generally, protection from excessive wear was best provided by those oils containing pre-dominantly alkyl ZDP (zinc dithiophosphate) antiwear additive instead of aryl ZDP. These results show that a laboratory engine test is needed to evaluate the long-term wear protection of engine oils.

To meet exhaust emission standards, nearly all 1975 model U. S. passenger cars use catalytic converters in conjunction with unleaded gasoline. While it has been established that lead and phosphorus from gasoline are deleterious to catalyst performance, much less is known about any similar effect of elements normally present in conventional engine oils. In addition, the ability to protect engines from excessive deposits and wear is essentially unproved for engine oils in which the phosphorus and metals contents have been either reduced (low ash oils) or eliminated (ashless oils). To obtain catalyst and engine performance information on such oils, tests were run using 95, 1972-1973 model passenger cars, operated with unleaded gasoline in several types of service. Forty cars were equipped with 1975 production-prototype underfloor catalytic converters containing pelleted oxidation catalysts.

Engine deposits and wear are greatly affected by engine oil-additive treatment variables and by engine-operating parameters, such as oil-change interval and oil filtration. While each of these two major elements has been investigated extensively, little is known about interactions between these elements. Tests with 1963-1967 model United States passenger cars, operating with leaded commercial gasolines in several types of service, evaluated effects on deposits and wear of: 1. Ashless (nonmetallic) dispersants. 2. Zinc dialkyldithiophosphate (ZDP) type and concentration. 3. Interactions between dispersant and ZDP. 4. Interaction among dispersant concentration, oil-change interval, and supplementary bypass oil filtration. Sludge and varnish deposit control differed widely among three dispersants used at equal concentrations. Increasing the concentration of the best dispersant reduced sludge but not varnish.

This paper reports the effects of fuels, lubricants, and their additives on deposit induced surface ignition in an automotive engine. The contribution of various elements commonly found in lube-oil additives and the effect of variations in base oil composition were studied in separate programs and subsequently combined. These data have been expressed quantitatively, using linear multiple regression equations. Some unusual results of additive treatment and of oil consumption rate on surface ignition are presented, and several anomalies in previous investigations by other workers have been resolved.

Vehicle emission control systems can markedly affect the environment within the engine crankcase, and could thereby increase engine deposits, wear, and oil degradation. Tests run using 1965-1970 model United States passenger cars, operating with leaded commercial gasolines in several types of service, evaluated the effects on deposits and wear of three types of experimental vehicle emission control systems: 1. Crankcase storage systems for reducing vehicle evaporative emissions. 2. An exhaust gas recirculation (EGR) system for reducing oxides of nitrogen. 3. Positive crankcase ventilation (PCV) systems for controlling crankcase emissions. In engines operated with production crankcase purging rates, crankcase storage increased engine rusting in short-trip service, and increased sludging and valve train wear in low-speed, stop-and-go service.

Surface ignition may be initiated by one of two mechanisms: mechanical hot spots or combustion-chamber deposits. Conditions determining whether or not surface ignition occurs and the surface ignition resistance of fuels are different for each mechanism. The occurrence of surface ignition may be detected by changes in engine noise, time of peak pressure, rate of pressure rise, or flame front propagation time. Surface ignition may cause decreased engine power, increased heat rejection, and, in severe cases, component physical damage and ultimate failure. Increased compression ratio, speed, and specific output all increase the tendency of an engine to experience surface ignition. The composition and additive treatment of both gasoline and crankcase oil have large effects on the surface ignition tendencies of accumulated combustion-chamber deposits.

Forty-one short-trip service tests were run using 1964-1969 model U.S. passenger cars and 19 commercial or experimental oils evaluating several aspects of engine rusting. These factors included differences in rusting severity among engine models, effects of fuel variables on rusting, and the effects of oil additive type and concentration on rusting. Rusting severity varied widely among engine models, but different engines ranked similarly the rust protection provided by oils with differing additive treatments. Use of either nonleaded gasoline or LPG instead of leaded gasoline greatly reduced engine rusting. At equivalent additive treatment levels, several magnesium sulfonates provided better rust protection than did certain calcium sulfonates, calcium phenates, or a barium sulfonate. Rust protection increased greatly and approximately linearly with increasing magnesium content.