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Engine oil specifications have been changing since the invention of the automobile and the internal combustion engine. The industry associations that have played a key role in engine oil specification development have changed or evolved in fairly regular time intervals. The specifications, the tests behind the specifications, and the groups involved in shaping the specifications are discussed from a historical and present day perspective.

Zinc dithiophosphate, or ZDP, for over 60 years has been used as an additive in engine oils to provide wear protection and oxidation stability in an efficient and cost effective manner. Unfortunately, ZDP contains phosphorus, and phosphorus is a widely known and accepted poison of automotive catalysts and other emissions system components. Because of this, phosphorus (and ZDP) levels in automotive engine oils have been gradually reduced by about 35% over the last 10-15 years, and further reductions are likely in the future. This paper traces the history of ZDP use in automotive engine oils, and addresses the issue of how much (if any) ZDP is actually required to provide wear protection in today's, as well as yesterday's, engines. The focus in the paper is on wear (including scuffing) protection, and not on the other aspects of ZDP performance, such as providing oxidation stability of the oil.

The effects of lubricating oil on friction and wear were investigated using light-duty 2.2L compression ignition direct injection (CIDI) engine components for bench testing. A matrix of test oils varying in viscosity, friction modifier level and chemistry, and base stock chemistry (mineral and synthetic) was investigated. Among all engine oils used for bench tests, the engine oil containing MoDTC friction modifier showed the lowest friction compared with the engine oils with organic friction modifier or the other engine oils without any friction modifier. Mineral-based engine oils of the same viscosity grade and oil formulation had slightly lower friction than synthetic-based engine oils.

The effects of lubricating oil on friction and engine-out emissions in a light-duty 2.2L compression ignition direct injection (CIDI) engine were investigated. A matrix of test oils varying in viscosity (SAE 5W-20 to 10W-40), friction modifier (FM) level and chemistry (MoDTC and organic FM), and basestock chemistry (mineral and synthetic) was investigated. Tests were run in an engine dynamometer according to a simulated, steady state FTP-75 procedure. Low viscosity oils and high levels of organic FM showed benefits in terms of fuel economy, but there were no significant effects observed with the oils with low MoDTC concentration on engine friction run in this program. No significant oil effects were observed on the gaseous emissions of the engine. PM emissions were analyzed for organic solubles and insolubles. The organic soluble fraction was further analyzed for the oil and fuel soluble portions.

The effect of engine oil aging on the fuel economy of two matched 1998MY Buick Centuries equipped with 3.1L engines but operating on different GF-3 prototype engine oils (one SAE 5W-20 engine oil and a second SAE 5W-30 oil) has been determined in EPA FTP testing. Combined FTP Fuel Economy for these vehicles was reduced at a rate of 0.06-0.12% per 1,000 miles of accumulation. The data for the various parts of the FTP test indicated differences in the loss of FE with use for the two vehicles. The vehicle with the SAE 5W-20 oil containing a Mo-type FM additive showed a lower decrease in FE with use during the cold transient than the vehicle with the SAE 5W-30 oil. On the other hand, the vehicle with the SAE 5W-30 oil containing an organic type FM additive and a balanced detergent/dispersant package showed a lower rate of decrease of combined FE with use than the vehicle with the SAE 5W-20 oil. These differences may be indicative of the different additive chemistry in these oils.

Gains in fuel economy with modern technology, SAE 5W-20 engine oils (GF-3 quality) in two identical 1998 MY Buick Centuries equipped with the 3.1L engine were measured in the EPA FTP test. These oils resulted in 1.0-2.2% gains in combined fuel economy (average 1.5%) over a typical GF-2 quality SAE 5W-30 oil. No significant gains in FE were observed during the cold transient portion of the FTP test. Engine oil temperatures were also reduced by 1-2°C with the SAE 5W-20 oils compared to the SAE 5W-30 oil. Of the two test oils, the one formulated with a Mo-type friction modifier additive was about 0.5% more fuel-efficient than the one formulated with an organic-type FM additive. Of the two vehicles, the one with the inherently poorer FE performance showed higher gains (expressed as percent improvement in FE) with the SAE 5W-20 oils than the other vehicle. Potential carry-over FE effects were observed with the oil containing the organic-type FM additive, but these effects were not verified.

Eight engine oils were evaluated in four GM vehicles in standard EPA fuel economy (FE), vehicle-dynamometer tests. The results were compared with the FE obtained with a standard ASTM reference oil (BC). The viscosity and the friction modification effects of engine oil on vehicle FE were quantified. Combined FE performance in the vehicles ranged from almost 2 percent improvement for an SAE 0W-10 oil, to over 1.5 percent poorer FE than the reference oil for an SAE 10W-40 oil. FE in three engines (3.1L, 3.8L, and 2.3L) showed a strong dependence on the viscosity of the oil (HTHS at either 100° or 150°C). This dependence was stronger during the city portion of the EPA test (lower temperatures) than the highway portion (higher temperatures). For the 5.7L engine no significant effect of oil viscosity on FE was observed although the highest FE seemed to be obtained at an HTHS (at 150°C) viscosity near 3.1 cP.

Nine engine oils were evaluated in two GM vehicles: a 1993 Pontiac Grand Am with a 2.3L Quad4 engine and a 1993 Buick LeSabre with a 3.8L (3800) V-6 engine. Standard EPA (Environmental Protection Agency) fuel economy (FE), vehicle-dynamometer tests were conducted. The results were compared with the fuel economy obtained with a standard ASTM reference oil (BC). The vehicle data from this program were used in evaluating the new engine-dynamometer ASTM Sequence VI-A test designed to predict “real world” fuel economy in vehicles. EPA 55/45 combined fuel economy performance in the GM vehicles ranged from almost 2 percent improvement (over the BC oil) for an SAE 5W-20 oil, to over 2 percent poorer fuel economy than the reference oil for an SAE 20W-50 oil. The two different engines responded similarly to the different oils and showed similar trends.

The emissions and performance of five diesel fuels, covering a range of cetane numbers and volatilities, were evaluated at three speeds and equivalence ratios in a single-cylinder, DI diesel engine. Graphical comparisons and regression analysis of the data revealed that cetane number and to a lesser extent volatility are the fuel parameters that most strongly influence emissions and performance, with higher cetane number and higher volatility fuels providing the best performance and lowest emissions. Trends toward lower cetane number, lower volatility fuels must be reversed to meet the emissions and performance standards of future light-duty DI diesel engines, should such engines be developed for use in automotive applications.

A symposium entitled: “The Relationship Between Engine Oil Viscosity and Engine Performance - Part VI” was held in Detroit, Michigan as part of the February 1980 SAE Congress and Exposition. Four of the papers presented at the symposium were bound in a booklet, SAE SP-460 and ASTM STP 621-S4. The discussions and author closures for these four papers as well as those for a paper presented in an earlier symposium are included in this paper and provide a supplement to the volume of bound papers.

To determine the correlation between journal bearing performance and viscosity loss in a capillary, viscosities of eleven base oil-polymer blends were measured in a high-shear, pressurized capillary viscometer (High-Shear Capillary Viscometer, HSCV) at shear rates from 100 to nearly 1 000 000 s-1. Although low-shear kinematic viscosities do not predict bearing performance differences found by Rosenberg with the same oil blends, HSCV viscosities at shear rates near 500 000 s-1 correlate well with the bearing performance data. Differences among polymers are strongly related to molecular weight.

An extensive effort is under way to revise the SAE Engine Oil Viscosity Classification System to reflect user needs more realistically. To understand how the present system evolved, the history of the classification is traced, from the original version first published in 1911 to the present 1976 version. Reasons for both high- and low-temperature viscosity grades, multigrading, and footnotes to the viscosity table are discussed, as well as other classification systems which have been discarded over the years. A critical assessment of the present classification is made from opinions offered at an SAE Open Forum last year. It is pointed out that the system has become quite complicated with four low-temperature and four high-temperature grades, five footnotes, and an appendix. Moreover, the high-temperature viscosity grades are based on an unrealistically low temperature of 98.9°C (210°F) and an unrealistically low-shear (kinematic) viscosity compared with engine operating conditions.

An analysis of oil pumpability reveals that engine oil pumping failures may occur because either the oil cannot flow under its own head to the oil screen inlet, or the oil is too viscous to flow through the screen and inlet tube fast enough to satisfy pump demands. To determine which factor is controlling, the behavior of commercial, multigraded oils was observed visually at temperatures from -40 to 0°F (-40 to - 17.8°C) in a laboratory oil pumpability test apparatus. Test results revealed that pumping failures occur by the first alternative: a hole is formed in the oil, and the surrounding oil is unable to flow into the hole fast enough to satisfy the pump. Of 14 oils tested, 7 failed to be pumped because of air binding or cavitation which developed in this manner. A model, which explains these failures in terms of yield point considerations and the low shear apparent viscosity of the oils, is proposed.