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A mechanism was proposed in SAE Paper #941983, (October, 1994) to explain why “Unique Boundary Chemistry” (UBC) described in said paper (1) required an extended conditioning period for its full antiwear benefits to be realized and (2) why the UBC Chemistry produced a strong antiwear carryover effect, even after relatively short exposure to the engine. This paper will document and discuss results from several metal surface studies employing a variety of metal surface analysis techniques (XPS, Profilometry, and AFM) to support various aspects of the earlier proposed antiwear mechanism. These surface analysis studies were carried out with pertinent boundary lubricated parts from (a) bench tests, (b) engines tested under modified protocol Sequence IIIE conditions described in SAE Paper 941983 and (c) standard ASTM Sequence IIIE and VE tests exposed to the UBC Chemistry.

Advances in Engine design such as fast-burn combustion and foul air ventilation have combined with higher blowby rates and smaller oil sumps to increase the sludge load on the lubricant. The nature of the sludge deposits has also changed from a soft to a significantly harder sludge. Progress has been made in understanding how oil-related deposits form in automotive engines. Engine deposits and used oil composition studies have supported the hypothesis that the oil's dispersant is rendered ineffective by greater interaction with the fuel blowby acids leading to increased and harder sludge deposits. Moreover, deposits/used oil analysis, using X-ray Photoelectron Spectroscopy (XPS), indicate that deposits precursors reside in the pentane insolubles of the used field engine oils. A bench test has been developed which simulates deposit formation in engines and which shows potential as a screener for the industry Sequence VE engine test.

An important quality feature of a crankcase engine oil is its ability to control oil consumption. To the average motorist low oil consumption is synonymous with the oil maintaining good engine performance, low levels of engine wear, low running costs and a clean driveway. In the current environment it has assumed major importance because of the possible adverse effect of oil consumption on exhaust emissions. An oil controls oil consumption by both its chemical and physical properties. Additive chemistry helps by minimizing piston ring and cylinder bore wear including bore polishing, the prevention of piston ring sticking and ensuring oil seals continue to work effectively. Tests to ensure control of these hardware variables were developed during the early 1980's. These test methods are briefly reviewed. Of the physical properties of an oil, viscosity and volatility are the two key characteristics known to affect oil consumption.

At SAE’s request, ASTM developed both an oil pumpability engine test and a bench test, the Mini-Rotary Viscometer (MRV). The MRV data correlated well with the full scale engine pumpability data. SAE then incorporated MRV requirements for Winter Grade oils into the Viscosity Classification System J-300 SEP80. A large number of engine oil pumpability failures occurred during the winter of 1980–81. In early 1981, ASTM, SAE and several companies started crash programs to solve the problem. These programs showed that those failure oils had a different sensitivity to cooldown cycle than the Pumpability Reference Oils (PROs) used in the original correlations. The cooldown cycle in the Federal Stable Pour Test appeared to better predict the 1980–81 failure oils, whereas the D3829 MRV cooldown cycle predicted the original PROs the best. Therefore, the Federal Stable Pour Test in combination with the Mini-Rotary Viscometer was recommended as a “stop-gap” measure.

Evaluation of the fuel economy characteristics of engine oils requires a rigorous test design. Side-by-side test designs, though adequate for evaluating the control of deposits, wear, and viscosity, require too many cars for precise fuel-economy testing. Crossover, Latin-square, and other balanced-block designs cannot be used if the fuel economy oil shows “carryover” effects; that is, if the engine is conditioned by the fuel economy oil so that subsequent oils still show a residual fuel economy benefit. The most suitable test design is a sequential one. The reference oil is run until it demonstrates a constant level of fuel economy. The test oil is then run for enough miles so that its full effect has been reached. The comparison is made between the two stabilized levels. Examples are given for an SAE 10W-40, API SF oil, which showed a 4+ % fuel economy improvement in both fleet and EPA type chassis-dynamometer sequential-design tests.

A new viscometer, the Mini-Rotary Viscometer (MRV), has been demonstrated to predict the low temperature pumpability performance of engine oils. This bench test method was developed at the request of SAE Fuels and Lubricants Subcommittee 2 and culminates a two-part ASTM Program to (1) define pumpability characteristics of reference oils in engines and (2) assess/develop bench test methods for predicting low temperature engine pumpability. The MRV is a low shear stress/shear rate viscometer that correlates either with an “average” engine or an individual engine, depending upon the critical rheological requirements of the particular engine or engines, and attains its high degree of correlation by predicting either of two failure modes-air binding of the pump or insufficient oil flow rate to the oil pump inlet. Thus, the MRV complements the Cold Cranking Simulator, a high shear stress device, in defining the low temperature behavior of straight-grade and multigrade engine oils.

A fuel-efficient passenger car engine oil has been developed that showed an average of 4.6% improvement in fuel economy compared with several premium, SAE 10W-40 oils (API Engine Service Classification SE) in a road fleet test. In the combined Environmental Protection Agency city/highway testing, this oil gave 5.5% better fuel economy on average than an SE premium 10W-40 oil. The excellent overall performance of this lubricant was confirmed by ASTM Engine Sequence tests and evaluation in severe taxicab operations. The new 10W-40 oil, which incorporates friction-reducing properties, is formulated with petroleum base stocks and known additives, many of which are conventionally used. It is expected that advances in friction-related technology developed in this work may lead to oils with even higher levels of fuel economy improvement in the future.