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In 2005, the growing emphasis on fuel efficiency coupled with the long-recognized negative effects of viscous friction caused by engine hydrodynamic lubrication, led to considerations of the benefits of lower viscosity engine oils by the SAE Engine Oil Viscosity Classification (EOVC) Task Force. More recently these considerations were given further impetus by OEM enquiry regarding modification of the SAE Viscosity Classification System to include oils of lower viscosity specification than that of SAE 20. For the EOVC Task Force, such considerations of commercially available, significantly lower viscosity engine oils, also produced a need to reassess the precision of high shear rate viscometry of such engine oils as presently practiced at 150°C - as well as interest in temperatures such as 100° and 120°C believed more representative of engine operating conditions.

Modern engines rely more and more on the engine oil to serve increasingly complex hydraulic functions such as, for example, controlling cylinder deactivation - a means of significantly increasing fuel efficiency. However, the success of hydraulic methods of activating mechanical responses in engines (or other devices) is dependent on the degree of incompressibility of the hydraulic fluid. As a consequence, those engine oil properties that impart susceptibility to foam formation in areas of hydraulic operations of the engine are detrimental to the engine's performance and durability. This paper is an initial study of aeration, air entrainment, and air release under pressure decrease using a simple bench test. The preliminary information reported suggests the potential application of the instrumental approach developed to measure the rate of foam formation from the air entrained in engine oils and the resistance of such foam to collapse.

Low-temperature engine oil pumpability has been a concern for OEMs, engine oil formulators, and additive manufacturers for a number of years particularly since a significant number of air-binding failures in 1980 and '81. On careful investigation of the cause of such field failures, it was found that oil sensitivity to a particular combination of weather conditions was responsible. The experience also suggested that many other low-temperature weather conditions might produce engine-damaging gelation. Thus, it seemed desirable to develop a bench test that would induce and measure gelation that might form in engine oil by continuously measuring slowly cooling oil over an extensive low-temperature range. This led to the development of the Scanning Brookfield Technique (SBT) first reported in 1982.

Viscometry has been closely associated with the lubricating properties of engine oils since the development of the reciprocating engine. With the advent of non-Newtonian multi-grade engine oils, a new dimension of viscometry was introduced - viscometry at high shear rates and high temperatures. In view of the importance of the critical hydrodynamic lubrication that engine oils provide - and the toll on engine efficiency that these oils extract - it was thought timely and practical to review the initiation and application of high shear rate engine oil viscometry and to discuss subsequent development.

Previous studies have shown that there is a lack of correlation between engine oil phosphorus volatility with both oil volatility and the initial level of phosphorus in the engine oil. On the other hand, these and more recent studies have illustrated that phosphorus volatility is related to temperature, other additives in the oil, and the chemical composition of the zinc di-organo di-thio phosphate (ZDDP) used. This paper reports the results of continued studies associated with engine oil phosphorus volatility, with the ultimate goal of reducing the amount of phosphorus that deposits on catalytic converters adversely affecting catalyst function.

The rheology and related low-temperature pumpability of engine oils used in modern heavy-duty diesel engines are markedly affected by the presence of high levels of soot. This paper presents results of studies of the rheological condition of highly soot-laden oils using two protocols of the Scanning Brookfield Technique as investigative tools.

Foaming of lubricating oil during operation of any automotive mechanism is undesirable. To control this problem, anti-foaming additives are often part of the formulated oil. However, during use, the oil contacts the gasketing material used to seal the mechanism and may extract pro-foamants in sufficient quantity to overwhelm the anti-foamant additive. Recognition of this problem has led to several different in-house tests of oil/gasket compatibility seemingly giving divergent information and technical direction concerning correction of foam-inducing factors of both the oil and gasket. It seemed appropriate to investigate and quantify the relative importance of several of the presumed influences on oil/gasket interaction. To do this, a relatively simple test simulating oil/gasket contact in the operating mechanism has been developed around an air foam-bath and applied in a series of Taguchi matrix studies to determine the influential factors.

The ability of engine oils to provide hydrodynamic lubrication under operating conditions is essential. Such lubrication occurs at very high shear rates -- often well in excess of the current SAE J300 specification of one million reciprocal seconds. This paper presents data obtained for shear rates beginning as low as two hundred thousand to above five million reciprocal seconds as well as the technique developed to obtain these shear rates.

Previous studies to improve upon the Noack volatility test have reported a new approach which does not require toxic Wood's Metal for heating yet agrees well with Noack test results. In addition, the new approach collects 99% of the volatilized oil for optional analysis. This can be important apropos to phosphorus levels which are of concern regarding automotive exhaust catalyst life. To more closely compare the new approach with the Noack test, reference oils used in a recent ASTM volatility round-robin study were analyzed and the new approach was found to produce close agreement with the Noack technique and generally greater repeatability.

This paper concerns a bench test developed to simulate the effect of engine operating conditions on the oxidation and deposit-forming tendencies of engine oils. The so-called Thermo-oxidation Engine Oil Simulation Test (TEOST) is carried out under temperatures and other environmental conditions identified as being significant in the internal combustion engine. These parameters can be readily modified to reflect different aspects of deposit conditions and/or different forms of the mechanical design of reciprocating engines. The most important aspect of the TEOST is the separation of the oxidation process into the two aspects believed to be present in the engine, (1) the preparation of oxidation precursors in the so-called ‘Reactor’ representing the engine sump and other moderately heated areas of oil exposure, and (2) the ‘Depositor’ representing those areas of the engine where temperatures are such that the completion of the deposit-forming oxidation mechanism can be induced.

Building on a previously presented concept of the Viscosity Loss Trapezoid (VLT), in this paper the author shows how the information contained in the VLT can produce a ‘viscous’ insight into the molecular weight distribution of an oil-soluble polymer such as a Viscosity Index Improver in formulated lubricants.

The author points out the necessity of a reevaluation of the SAE J300 Engine Oil Viscosity Classification System and of the instruments and bench tests developed over the last 30 years to predict low-temperature engine oil performance. Greater ease in starting engines at low temperatures as a consequence of lower friction, electronic timing, and fuel injection has resulted in engines with potentially much higher Critical Starting Viscosities than those which formed the basis for the low-temperature portion of the SAE J300 Classification System. Presenting some of the pertinent low-temperature data available from a well-known engine oil database, the author discusses the consequences of this situation with regard to a number of questions related to the present application of pumpability and startability bench tests, their limitations, and the importance of finding ways to meet the technical challenges.

Scanning Brookfield Technique (SBT) studies have provided the background for a new concept in rheological characterization of gelation in lubricating oils at lower temperatures. Using the typical SBT temperature/viscosity range, the concept requires calculation of the first derivative of the MacCoull/Walther/Wright empirical equation. The derivative values show peaks at the temperatures at which gel formation begins and these peak heights, which are termed the Gelation Index, are shown to correlate with values of yield stress from the literature. They are also shown to correlate with the presence and severity of air-binding pumpability failure in the field and in the ASTM Pumpability Studies.

The Scanning Brookfield Technique (SBT) is used to examine the nature of air-binding, pumpability problems. Causes of the failure of the first ASTM pumpability test methods are examined and used to caution present and future assumptions subtly but markedly affecting test method development. The engine itself may, by its design, be super sensitive to the occurrence of even moderate oil gelation, raising the question of gelation-prone oils vs. gelation-sensitive engines. Dialysis experiments showed that oil additives could sometimes cause gelation as well as prevent it.

The authors' present low-shear, low-temperature studies on engine oils obtained by a new technique utilizing a SIVERSO programmable cold-bath in conjunction with the Brookfield LVT viscometer. The Brookfield/SIVERSO technique seems to respond sensitively to the yield stress of gelled engine oils. The relatively simple technique predicts the Borderline Pumpability Temperature of both air-binding and flow-limited engine oils with reasonably good correlation. Lastly, a preliminary examination of the agreement of the new technique with the conventional, air-bath Brookfield technique is shown. The correlation is very good and suggests that the Brookfield/SIVERSO technique may have wider automotive applications.

It has long been known from various sonic and mechanical shear tests that most commercial multigraded oils suffer from a serious loss in viscosity during relatively short periods of use. These tests, except in special cases, were generally regarded as inadequate. In order to conduct a meaningful study of the effect of shear degradation on polymer-containing oils, the authors set up an engine test. The test, over a period of several months using three engines almost daily, proved reliable beyond all expectations. Tests of 15 different multigrade oils showed that seven did not qualify as SAE 30 oils after a running period equivalent to about 385 miles. All the remaining oils showed significant losses in viscosity in the same period. The effect of shear degradation on the 0°F measured viscosity was varied. Most of the oils showed a proportionately lower viscosity loss measured at 0°F than at 210°F. Complicating factors indicate that the area merits further investigation.

This paper presents a progress report on the development of low temperature viscometric techniques by ASTM Section B on Flow Properties of Non-Newtonian Fluids. These techniques are based on engine cranking studies obtained by the Coordinating Research Council. Two techniques involving three viscometers are reported.

Recent cold-room studies have shown that the importance of engine oil viscosity is not in controlling engine cranking speed but in absorbing power from the starting engine. Cranking speed itself appears to be merely an index of engine oil viscosity. It is shown that engines may be successfully started at cranking speeds as low as six rpm if the viscosity of the engine oil is suitably low. On the other hand, if the viscosity of the engine oil is too great the engine may start but will not continue to run even at cranking speeds as high as 125 rpm. These findings are important as they indicate that low-temperature starting cannot necessarily be improved by the simple expedient of increasing the starting system capacity. Rather, good low-temperature oil viscosity is required.

A LOW-TEMPERATURE study of the relationship between the performance of a step-type automatic transmission and the transmission fluid viscosity is reported in this paper. It is shown that the low-temperature malfunction of these units is due to the viscometric properties of the fluid and that at the temperature at which the fluid reaches a certain critical viscosity the transmission will fail. A mathematical analysis of the mechanism of failure supports the conclusions drawn from the experimental study.*

The behavior of motor oils at low temperatures is obviously important to the performance of the motor. Low temperature cranking speeds have been shown to be dependent on the viscosity, and in a previous paper the author has shown that the viscosity characteristics of motor oils at these temperatures may be unusual, especially when they contain Viscosity Index Improvers. In this paper the author has analyzed the results of 250 cranking tests conducted at temperatures from +3° to −35°F. These results were compared using the viscosities as determined in a moderate shear viscometer and as extrapolated and calculated by the ASTM chart and a recently published analytical technique.