PART II
`APPLICATIONS
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`ORONITE EXHIBIT 1009
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`19
`Automotive Crankcase Oils
`
`Stephen C. Lakes
`Henkel Corporation/Emery Group
`Cincinnati, Ohio
`
`INTRODUCTION
`I.
`Crankcase engine oils are the most recognizable lubricant in the automotive area. Both the indi-
`vidual and the commercial consumer equate vehicle lubrication with the engine oil. Millions in
`advertising budget are spent worldwide to promote specific brands in this area. The engines them-
`selves and the crankcase lubricants protecting them have been upgraded over the last two decades
`such that engine life for gasoline passenger cars up through heavy-duty diesel trucks is longer
`than ever before.
`Synthetic engine oils have been commercially marketed since the 1960s but have taken only
`a small share of the large engine oil market, worldwide. The European passenger car motor oil
`(PCMO) market utilizes the highest proportion of full or partially synthetic engine oils, with the
`North American and Far Eastern areas lagging behind on synthetic use for this application.
`Synthetic-based oils exhibit improved viscometric, volatility, and thermal stability properties
`over conventional petroleum-based oils. Improved engine tolerances, governmental emission
`regulations, and the corporate average fuel economy (CAFE) requirements in the United States
`are promoting improved performance engine oils and more stringent base stock requirements.
`Synthetics will play a future role both in full synthetic formulations and as base stock or additive
`component in PCMO and heavy-duty diesel oil (HDDO) partial synthetic oils.
`
`A. Engine Oil Applications
`There are several variations of internal combustion engines used as automotive power plants.
`Some use an oil sump or reservoir, and others use an oil/fuel mix for lubrication. Those engines
`with “crankcase fill” systems include four-cycle gasoline engines, four-and two-cycle diesel
`engines, and unconventional fueled engines (natural gas, liquid propane, alcohol, or vegetable
`oils). This chapter concentrates on crankcase oil lubrication systems. Outboard engines and
`engines for two-cycle motorcycles and recreational vehicles, where the internal moving parts are
`lubricated by oil injection or oil/fuel mixtures, are not considered.
`In crankcase fill engines, the lubricant is stored in the engine sump and is pumped or
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`splashed onto the various moving parts during operation. The function of the engine oil
`encompasses lubrication of moving parts, friction reduction, wear reduction, cooling of internal
`components, and collection of combustion by-products for removal. By-product removal is
`accomplished by in-system filtration of the oil and/or a final drain of the used lubricant. Current
`automotive gasoline engines have an operating life of approximately 3000 hours and will use
`about 150 L of engine oil during that time. Most four cycle passenger car engines are scrapped for
`metal recycle, not rebuilt. On the other hand, heavy-duty diesels for commercial over-the-road
`trucks will last approximately 15,000 hours and use around 2000 L of engine oil prior to rebuild.
`Preliminary studies of unconventional fueled engines have shown comparable operating life and
`oil consumption compared to gasoline- or diesel-fueled counterparts.
`Internal combustion engine life is measured as the operating hours before overhaul or engine
`replacement. The primary areas for engine overhaul are the main bearings, the piston rings, and
`the cylinder walls. Excessive wear of the crankcase bearings will result in insufficient oil pres-
`sure in the internal galley and low oil delivery to the upper portion of the engine, leading to accel-
`erated wear and shortened life. Ring wear or sticking will result in power loss due to blowby and
`cylinder pressure leakage. Wear or glazing of the cylinder walls will result in excessive oil burn-
`ing and subsequent power loss.
`The expectations for extended engine life of the individual or fleet operator are reflected in
`increased awareness of engine oil performance. Improved cold weather starting, lower oil loss
`during operation, and engine cleanliness are attributes that the consumer recognizes and demands
`of today’s oils. Combined with longer warranty protection from the equipment manufacturer,
`these factors present an opportunity for synthetic base stock use. Synthetics can be added to
`improve mineral oil based formulations or used to make top tier fully synthetic oils.
`
`B. Performance Requirements for Engine Oils
`The viscometric requirements for engine oils are categorized and defined in a group of vis-
`cosity grades defined by the Society of Automotive Engineers under “SAE Viscosity Grades
`for Engine Oils” (see Table 1). The same document also gives the performance of engine oils
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`of different viscosity grades with respect to the high temperature/high shear requirements of
`the American Society for Testing and Materials (ASTM) and the Coordinating European
`Council (CEC) (see Table 2).
`The predominant gasoline engine oils, in use, are the 5W-30 through 10W-40 multigrade
`oils. Passenger and heavy-duty diesel engine oils are mostly 10W-40 and 15W-40 viscosity
`grades.
`After the viscosity grade has been defined, crankcase engine oils are classified into two
`major categories:
`
`gasoline engine oils: API S (service category of the American Petroleum Institute) and A-96
`(European passenger car classification from ACEA, the Association des Constructeurs
`Européens)
`diesel engine oils: API C (commercial category). B-96 (European passenger diesel), and E-96
`(European heavy-duty diesel)
`
`Alternative fuels, listed and defined in the “Alternative Automobile Fuels,” (SAE J1297,
`March 1993), and include liquid propane gas, ethanol, methanol, compressed natural gas, ethers
`(e.g., methyl t-butyl ether, t-amyl methyl ether), and higher molecular weight alcohols. No spec-
`ified oil categories are available at this time for these fuels. The matter is currently under review
`by the SAE.
`
`C. Requirements for Gasoline Engine Oils
`North American gasoline passenger car oils fall under the API and ILSAC categories. The API
`SJ service category (adopted in 1996) and ILSAC GF-2 are comprised of a set of engine tests for
`defining minimum oil performance:
`
`Sequence L-38: uses a single-cylinder test engine (42.5 CID). This test evaluates an engine oil’s
`performance in resisting copper, tin, and lead bearing wear and corrosion in the engine, and
`viscous shear loss in the lubricant.
`Sequence II-D: uses a 1978 General Motors eight-cylinder commercial engine (350 CID). This
`test evaluates an engine oil’s performance in resisting internal engine corrosion, specifically
`the valve pushrods, hydraulic valve lifters, and oil pump relief valve.
`Sequence III-E: uses a 1986 General Motors V-block six-cylinder commercial engine (231 CID).
`This test evaluates an engine oil’s ability to resist sludge formation and cam lobe and lifter
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`wear in the engine, as well as high temperature oxidation (Kinematic viscosity increase at
`100⬚C) in the lubricant.
`Sequence V-E: uses a Ford four-cylinder commercial engine (2.3 L). This test evaluates an engine
`oil’s ability to resist sludge and varnish formation, overhead valve wear in the engine, and
`formation of degradation/wear products (Kinematic viscosity increase at 100⬚C Fe, Cu, Si,
`pentane insolubles; fuel dilution) in the lubricant.
`Sequence VI-A: uses a 1993 Ford eight-cylinder commercial engine (4.6 L). This test evaluates
`the effect of the engine oil on gasoline fuel economy compared to a reference oil.
`
`Tentative European gasoline oil categories were introduced by ACEA in 1994 as replace-
`ments for the G-4 and G-5 oil categories. These were finalized in December 1995 and became
`effective in early 1996. The gasoline engine oil categories are:
`
`A1-96 Current Quality
`A2-96 Extended Drain
`A3-96 High Tier, Extended Drain
`
`These categories are defined as minimal by the ACEA:
`
`These sequences define the minimum quality level of a product for presentation to ACEA
`members. Performance parameters other than those covered by the tests shown or more strin-
`gent limits may be indicated by individual member companies.
`
`Most European OEMs require additional engine testing for specific usage and warranty
`application.
`Engine tests for minimal oil performance for ACEA include the following.
`
`Sequence III-E: same as API SJ.
`Peugeot TU3M High Temperature Test: uses a modified Peugeot TU3M/KDX in-line four-cylin-
`der engine (1.3 L). This test evaluates an engine oil’s ability, under high temperature, high
`speed conditions, to resist ring sticking and piston deposits in the engine and viscosity
`increase in the lubricant (procedure listed as CEC L-55-T-95).
`Peugeot TU3M Wear Test: uses a Peugeot TU3M/KDX commercial four-cylinder engine (1.3 L).
`This test evaluates an oil’s ability, under slow and moderate speed/low temperature condi-
`tions, to resist valve train wear (procedure listed as CEC L-38-A-94).
`Sequence V-E: same as API SJ.
`MB M111 Black Sludge Test: uses a Mercedes-Benz M111 E20 four-cylinder commercial engine
`(2.0 L). This test evaluates an oil’s ability, under varied driving conditions (urban to auto-
`bahn), to resist sludge formation in the cylinder head area, as well as piston varnish forma-
`tion and ring sticking in the engine. The lubricant is tested for viscosity change, fuel dilu-
`tion, total base number (TBN), sulfated ash, solids, and wear metals (procedure listed as
`CEC L-53-T-95).
`MB M111 Fuel Economy Test: uses a modified Mercedes-Benz M111 E20 four-cylinder engine
`(2.0 L). This test evaluates the effect of the engine oil on gasoline fuel economy compared
`to a reference oil (procedure listed as CEC L-54-X-94).
`
`The ACEA A gasoline engine oil categories also include bench testing for shear stability, high
`temperature/high shear (HTHS), NOACK volatility, sulfated ash limits, foaming properties, and
`elastomer compatibility limits.
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`D. Diesel Engine Oils
`North American diesel engine oils are predominantly for heavy-duty commercial use. The API
`CF-4 and CG-4 commercial categories and the MIL-L-2104F military category use a set of
`engine tests for defining minimum oil performance. The most current and stringent category,
`API CG-4, uses two test sequences built around the same rigs and conditions as the SG gasoline
`engine oil tests, these include the CRC L-38 and Sequence III-E (described in Section I.C). The
`CG-4 also requires three more tests, as follows.
`
`Caterpillar IN: uses a single-cylinder Caterpillar test engine (148.8 CID). This test measures an
`oil’s ability to resist formation of excess piston deposits, specifically the top land and top
`groove areas of the piston. The oil consumption is also measured, in grams per kilowatthour.
`Mack T-8: uses Mack E7-350 six-cylinder commercial diesel engine (11.93 L). This engine test
`measures an oil’s ability to resist viscosity increases due to excessive soot formation. The
`engine oil is measured for viscosity increase, soot loading, maximum oil pressure drop at the
`filter, and oil consumption.
`GMPT 6.2 L: uses a General Motors commercial engine (6.2 L). This test measures an oil’s abil-
`ity to give protection from roller follower wear in the engine.
`
`The CG-4 test program also involves the Cummins Corrosion Bench Test, the D-130 Copper
`Corrosion Test, and the ASTM D-892 Foam Test (Sequences I–IV).
`Currently, the industry is laying the groundwork for the next generation of diesel engine cat-
`egories (API PC-7 and PC-8). Driving both the North American and European changes are the
`more stringent emission requirements imposed by national legislatures. U.S. Federal Regulations
`mandate the profile shown in Fig. 1.
`The engineering challenge associated with these changes reflects the reluctance of OEM and
`end user alike to accept shorter drain intervals or shortened engine overhaul life. The industry is
`pushing for both extended oil drains and maintaining engine life.
`European diesel engine oils are designated for light to medium duty use or medium to heavy
`duty use. The ACEA members are using the following temporary designations for the develop-
`ment of the light-duty diesel categories (for passenger cars and vans):
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`B1-96 Current Quality/Economy
`B2-96 (PD-2) Extended Drain
`B3-96 (High Tier, Extended Drain
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`Lakes
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`Engine tests for minimal oil performance include the following:
`
`MB OM 602A: uses a Mercedes-Benz commercial engine (2.5 L). This test serves for all three
`categories and measures an oil’s ability to resist cam wear, bore polishing, sludge formation,
`and excessive oil consumption in the engine, as well as cylinder cleanliness. The engine oil
`is measured for viscosity increase and wear metals (procedure listed as CEC L-51-T-95).
`VW 1.6 L TC: uses a TC intercooled Volkswagen commercial diesel engine (1.6 L). This test
`measures an engine oil’s ability to resist ring sticking and to maintain piston cleanliness
`under high temperature conditions (procedure listed as CEC L-46-T-93).
`XUDllATE: uses a Peugeot commercial diesel engine (2.09 L). This test measures an engine oil’s
`ability to resist ring sticking and to maintain piston cleanliness (merit system). The engine
`oil is measured for viscosity increase under soot loading conditions (procedure listed as CEC
`L-56-T-95).
`
`For the development of heavy-duty diesel (trucks and off-road equipment) categories, ACEA
`is using the following temporary designations:
`
`El-96 Current Quality
`E2-96 Extended Drain Euro I
`E3-96 Extended Drain Euro II
`TD-4 Next Generation/Under Development
`
`Engine tests for minimal oil performance include the following:
`
`MB OM 602A: same test platform and conditions as B-96 categories.
`MB OM 364A: uses a Mercedes-Benz commercial diesel engine (3.97 L). This test, used in all
`three categories with different passing criteria, measures an oil’s ability to resist bore polish-
`ing, piston varnish/deposits, sludge formation, cylinder wear, and excessive oil consumption
`(procedure listed as CEC L-42-A-92).
`Mack T-8: see North American CG-4 category, above.
`
`Both the B-96 and E-96 categories also evaluate shear stability (Bosch injector), HTHS viscosi-
`ty, NOACK volatility, sulfated ash, foaming properties, and elastomer compatibility. Most
`European OEMs also require additional engine testing for specific usage and warranty
`applications.
`
`II. HISTORICAL ASPECTS OF SYNTHETIC ENGINE OILS
`A. Early Fluids
`Synthetic hydrocarbons and esters for engine lubricants were initially researched in the 1920s and
`1930s. Both F. W. Sullivan et al. of Standard Oil in the United States [1,2] and Zorn of I. G.
`Farben in Germany [3] were investigating the polymerization of olefins to form improved engine
`oil base stocks. These were the first synthetic hydrocarbons comparable to the poly(␣-olefins)
`(PAOs) of today. Ester base stocks were also under development at the same time for improved
`low temperature properties. These synthetic base stocks never realized significant engine oil
`commercialization for economic and supply reasons.
`During the 1940s, with the development of the turboprop and jet turbine aircraft engines,
`interest in ester lubricants was renewed. However, it was not until the 1960s, with the impetus
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`of military and construction requirements for arctic conditions, that synthetic engine lubricants
`had a resurgence. In the 1970s, with higher crude oil prices, interest developed in synthetic
`engine oils for the commercial market. These formulations used ester base stocks initially and
`later used PAOs in full and partial synthetic formulations. In the 1970s, several engine oil pro-
`ducers in the United States marketed products for passenger car engine oils. Synthetic products
`were also developed and marketed in Europe and Japan during this time.
`Worldwide, synthetic engine oils were very slow to be accepted and still comprise a
`small market share. Engine manufacturers are beginning to recognize the benefits of fully
`and partially synthetic oils.
`
`B. Need for Synthetic Engine Oils
`There are only three reasons for a consumer to use a synthetic or partial synthetic engine oil.
`
`It solves a technical problem.
`1.
`Its use results in improved economics.
`2.
`3. Governmental regulations.
`
`Technical requirements may involve using synthetics to satisfy high or low temperature proper-
`lies, to improve oil durability, or to improve engine test performance. In Europe, the addition of
`PAO and ester base stocks has allowed oil formulators to increased thermal/oxidative stability
`requirements and to achieve improved volatility specifications and better low temperature start-
`ing. In North America, OEMs are requiring more stringent lubricant performance in engine clean-
`liness, as well as improved volatility and low temperature pumping/starting. OEMs are starting
`to specify synthetic engine oils for some high performance applications (e.g., GM’s Chevrolet
`Corvette).
`Full synthetic arctic engine oils have been used by the U.S. military, NATO, and civilian
`companies since the early 1970s for equipment serving in extreme cold weather conditions
`MIL-L-46167B).
`The use of synthetics in engine oils has just started to show economic justification in the mar-
`ketplace. The consumer—whether an individual with a passenger car, a leasing company with
`return vehicles, or a business with a fleet of trucks—is beginning to recognize the economic
`advantage of increased engine life that is associated with the use of high performance oils. This
`advantage can be shown for extended vehicle service or residuals on resale.
`High performance, heavy-duty diesel engine oils are under development and testing to
`extend the oil drain interval and to lower maintenance costs, while maintaining or increasing
`engine operating life. Synthetic components (PAO, diester, polyol esters) are being evaluated in
`conjunction with high performance additive systems for this “next generation” HDDO. These
`components are being added at 5–30 wt % with petroleum base stock for enhanced additive and
`by-product solubility, improved engine cleanliness, good viscometric properties, and lower oil
`volatility.
`Worldwide, government regulations are starting to reflect concerns with vehicle fuel
`usage and the environmental impact of the products of the internal combustion engine. These
`regulations are affecting vehicle and engine design and formulations for the lubricants used
`in these vehicles. Fuel economy has been subject to government guidelines since the 1970s
`(CAFE in the United States). Heavy-duty diesel emissions guidelines in 1978, 1994, and 1998
`in North America and corresponding requirements in Europe and the Far East are changing
`the engines and oils. All these requirements are designed to promote more efficient energy
`usage and to diminish the environmental impact of these engines.
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`III. TYPES OF SYNTHETIC
`A. Definition
`In no other area of lubrication has the definition of “synthetic” generated as much debate or confu-
`sion as in engine oils. Technical definitions are being combined with performance attributes to pro-
`mote highly modified petroleum oils as a “synthetic” or “synthetic performing” product. The reasons
`are economic and are related to business goals. The use of the label “synthetic” has a high perform-
`ance connotation for the engine oil consumer and can justify a higher price. In this chapter, “synthet-
`ic” refers to a technical category. According to the ASTM, a synthetic lubricant is “a product which
`consists of stocks manufactured by chemical synthesis and containing necessary performance addi-
`tives.” To the chemical technologist, synthesis involves taking smaller chemical building blocks and
`combining them in a predictable, ordered reaction to form precise larger molecules.
`
`B. Synthetic Base Stocks
`For engine oils, the term “synthetic” refers to the base stock portion of the compounded oil. The
`additives and any polymers present are usually considered synthetic, being synthesized for spe-
`cific chemical purposes. The base stock constituent can be made from petroleum or synthesized
`structures (Fig. 2) or a combination of the two.
`The predominant synthetic base stocks currently used in engine oils are PAOs and carboxylic
`acid esters (diesters, polyol esters, or complex esters). Other synthetics include polyalkylene gly-
`cols (PAGs), phosphate esters, silicones, and alkylated aromatics, but these constitute only a
`small market share and, if used, are present only at additive levels in commercial engine oils.
`PAOs and esters may be used at various levels in gasoline and diesel engine oils. Most oil
`formulators consider up to 10% as an additive level treatment and 10% or higher as a base stock
`addition.
`Full synthetic gasoline engine oils are usually all PAO or a PAO/ester mixture. Full synthet-
`ics using all-ester base stock were developed and marketed in the 1970s. These oils showed good
`thermal stability and cleanliness, but seal and petroleum oil compatibility questions relegated them
`to small-niche, specific-use areas. The all-PAO and PAO/ester synthetic gasoline engine oils do not
`exhibit these deficiencies and are being successfully marketed throughout the world. Full synthet-
`ic diesel engine oils have been developed but have attained little market share for reasons of cost.
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`Partial synthetics utilize the addition of PAO, ester, or PAO/ester combination to enhance
`performance characteristics. Typical levels are 5–30 wt % in petroleum. Compared to conven-
`tional and unconventional petroleum oils (CBOs and UCBOs), PAO or ester may contribute
`desirable performance properties to the formulated oil, as indicated in Fig. 3.
`Most additive systems for engine oils were developed for a petroleum-based system and
`may not be suitable for synthetic oils. Additive selection for synthetics and partial synthetics is
`affected by the type and quantity of the base stock present. As a rule, PAO formulations show
`lower solubility for the polar additive packages than is found with petroleum. These polar addi-
`tives moderate detergent, dispersant, TBN, antiwear, and anticorrosion performance properties.
`The engine oil formulator may have to consider screening for acceptable additives or incorpo-
`rating longer alkyl chains on the additive molecules. Ester-containing formulations usually show
`higher solubility for these polar additives than is found with PAO or petroleum base stocks. A
`combination of PAO and ester may be used to “dial in” a specific polarity index to the base stock
`to maximize additive and by-product solubility. Elastomer compatibility (seals, gaskets) may
`also be accurately defined with a mixed PAO/ester system without the use of a seal swell agent.
`Polymers used for viscosity index improvement or thickening can also be affected by the
`base stock type. The use of PAO or ester can alter the polarity of the oil sufficiently to impact
`compatibility of some oligomers. In evaluating an unknown system or polymer, all formulated
`oils should be fully tested for storage and for high and low temperature compatibility as part of
`the testing regime.
`
`IV. COMPARATIVE PERFORMANCE DATA
`A. Bulk Physical Properties
`The predominant viscosity grades for synthetic base stocks in engine oils are 4 to 6 cSt (at
`100⬚C). This conforms to 100–200 SN petroleum oil. PAOs and esters (diester, polyol ester) usu-
`ally show improved viscometrics, higher viscosity index, improved low temperature properties,
`and lower volatility, compared to petroleum base stock, (Figs. 4 and 5).
`
`B. High Temperature Performance
`Automotive synthetic base stocks (PAO and ester) exhibit improved high temperature properties
`versus petroleum oils of comparable viscosity. These improvements are characterized by viscos-
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`ity retention at high temperature (due to a higher viscosity index), higher flash points, and lower
`volatility.
`Higher viscosity index base stocks, whether petroleum or synthetic, will exhibit lower vis-
`cosity loss upon temperature increase. This property will translate into higher film strength for
`hydrodynamic and elastohydrodynamic lubrication in the engine. At high temperatures this set of
`characteristics will mean improved protection for bearings (sleeve, ball, or needle) and rotating
`seals. High temperature/high shear is a test method for predicting viscosity effects for bearing
`wear for automotive engine [4]. Higher wear protection (boundary lubrication) for cams and
`valve lifters usually is handled by the antiwear additives present.
`Flash points are performed on engine oils to measure their flammability limits for storage
`and handling. Shipping requirements of the U.S. Department of Transportation (DOT) and OEM
`safety guidelines limit the flash points for commercial gasoline and diesel engine lubricants. The
`predominant test utilized for engine oils is the ASTM D-92 Cleveland open cup (COC) method.
`Petroleum-based oils have a wide range of molecular weights within a distillation fraction.
`By contrast with these refined base stocks, synthetic base stocks are more highly controlled
`for structures and composition. This results in tighter molecular weights and lower extraneous
`functional groups present, which may impact flash points. As shown in Figs. 4 and 5, PAOs
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`and esters exhibit higher flash points than petroleum base stocks of comparable viscosity. Esters,
`which contain polar functional groups, will exhibit higher flash points than petroleum or PAO
`feeds of similar molecular weight. This property is due to hydrogen bonding on the molecular
`level. Care must be exercised in the preparation and refining of esters to ensure low levels of
`unreacted acids or alcohols. These low molecular weight components will have a significant
`impact on flash point.
`Addition of synthetic components to petroleum-based engine oils will do little to improve
`the flash point. Full synthetic engine oils usually exhibit the best flash point properties. Fire
`points (temperature at which an oil will sustain combustion) is similar for petroleum-, PAO-, or
`ester-based engine oils of the same molecular weight.
`Engine oil volatility is a measure of an oil’s resistance to evaporation under high tempera-
`ture operating conditions. This is an important property for an engine lubricant because the loss
`of lower molecular weight components can significantly impact the viscosity properties. A 5W-
`30 oil that shows excessive volatility loss may end up being a 10W-40 or higher viscosity grade
`oil after several hundred miles of service. A correlation has been established between NOACK
`volatility and oil consumption [5].
`Several methods are used for measuring volatility, including the ASTM D-2887 distillation
`method and the CEC L-40-T-87 NOACK volatility test. Synthetic base stocks have lower volatil-
`ity losses by both methods [6]. (Figures 4 and 5 show comparative NOACK volatility data.) The
`addition of synthetic base stock can impact the overall volatility properties, even with small lev-
`els. The resulting final volatility will be approximately the algebraic calculation of the two com-
`ponents. Petroleum-based engine lubricants can be topped off with PAO or ester to shift the
`volatility into the passing range (Fig. 6).
`Both petroleum and synthetic low volatility base stocks have been investigated with a view
`to formulating lower volatility engine lubricants [7].
`
`C. Low Temperature Characteristics
`Full synthetic engine lubricants offer excellent low temperature flow and viscosity properties.
`PAO and ester base stocks show significantly lower pour points than petroleum oils (see Figs, 4
`and 5). This advantage is due to molecular structure and to the lack of crystalline wax particles,
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`present in some refined petroleum oils. These lower pour points translate into better low temper-
`ature flow and protection in both gasoline and diesel engine oils. Low temperature flow proper-
`ties may be measured in gasoline and diesel engine oils using laboratory viscosity methods
`(ASTM D-5293; Cold Crank Simulator, ASTM D-4684; MRV Pumping, Scanning Brookfield
`Viscosity), cold box simulation testing, and field conditions [8–12].
`The low pour properties of the synthetic base stocks allow the formulator a tool for adjust-
`ing petroleum-based engine oils for improved low temperature properties. Both PAO and ester
`may be used to achieve this improvement. For example, the addition of PAO (PAO-4) to a 5W-
`30 petroleum-based engine oil resulted in improved low temperature viscosity and pour points
`(Figs. 7 and 8).
`Typical petroleum-based engine oils contain pour point depressants that interrupt the crystal
`lattice formation of the wax content. The addition of synthetic base stock usually allows the
`removal of the pour point depressant from the additive package. Some low temperature compat-
`ibility problems (e.g., slight hazing or precipitate floc of the pour point depressant under low tem-
`perature, long-term storage) have been experienced with the use of certain pour point depressants
`and synthetics.
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`Specialty arctic engine oils have been developed for very low temperature usage, predomi-
`nantly for the military and the oil exploration industry. Full synthetics have been used for these
`applications since the mid-1970s and constitute the majority of these fluids designed for cold
`weather environments.
`
`D. Antiwear Performance
`Engine oils require a certain level of antiwear capability. This antiwear requirement ensures an
`oil’s ability to protect moving parts (e.g., rocker arm contacts, cams, cylinder ring/wall contact
`areas) under boundary lubrication conditions. In modern engine oil formulations, antiwear capa-
`bility is predominantly supplied by the additive package. The base stock portion, either petroleum
`or synthetic, has little antiwear capability. Petroleum oils may have a small amount of antiwear
`present as trace levels of sulfur, nitrogen, or phosphorus functionality from the crude petroleum
`source, but they contain an insufficient amount to provide protection for modern engines.
`The use of PAO or ester may require a higher uptreat of antiwear additive to compensate for
`the absence of these “natural” additives. PAO will be similar to petroleum for the treat level effect
`of most antiwear additive systems. Ester-containing engine oils may require an uptreat of anti-
`wear additive to achieve the same level of protection as petroleum-based systems. Esters are
`more polar than both petroleum and PAOs and may compete at the metal surface with any polar
`additives (antiwear agents, corrosion inhibitors, etc.).
`
`E. Shear Stability
`Most multigrade gasoline or diesel engine oils use a viscosity polymer for thickening the oil and
`improving the viscosity index. This allows the formulation of a cross-graded product that
`exhibits good viscometric profiles both at high temperatures (at operating conditions) and at low
`temperatures (during starting). The introduction of viscosity polymers required the industry to
`evaluate the properties of temporary and permanent viscosity loss under various shear condi-
`tions. High temperature/high shear (HTHS, ASTM D-4624 and D-4683) is used to measure the
`temporary viscosity loss under high shear load, which simulates the condition of the oil in the
`crankshaft bearings. The use of synthetic base stocks, with their higher viscosity index, may
`improve the HTHS slightly, but this effect is usually small compared to the contribution of the
`viscosity polymer.
`Permanent shear loss is measured by subjecting the motor oil to a shear force sufficient to
`cause breakage of the polymer structures, resulting in viscosity loss. Several procedures are avail-
`able for shear stability testing for engine oils. These include sonic shear (ASTM 2603), Orbahn
`shear (D-3945) and Bosch injector (CEC L-14). Synthetic automotive base stocks (PAOs, esters)
`are similar to petroleum and show little or no viscosity loss under these