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Some of the properties intrinsically present in the backbone of polyalkylene glycols (PAGs), which have nowadays attracted the automotive original equipment manufacturers (OEMs), are presented, such as bio-no-tox properties, heat capacity, extended drains, low friction, low AlSi-liner wear, fuel economy, and very high viscosity indices, and are achieved with metal-, ash-, and polymer-free formulations, which guarantee no adverse contamination of the lambda sensor and the active centers of the catalyzer as well as not to increase the exhaust back pressure of the particulate filter through ash deposits. This paper illuminates the latest results from OEM’s engine bench and road testing supporting the following functional benefits: (a) bio-no-tox, (b) improvements of fuel economy, even when compared with latest hydrocarbon-based prototype oils, (c) reduced wear, (d) reduced engine friction, (e) extended drains, (f) suited for bio-fuels, (g) no adverse effects on after-treatment devices through ash-, metal-, and polymer-free formulations, etc.

Low-temperature viscosity of engine oils is a key indication of a lubricant’s capacity to provide wear protection during starting and subsequent operation of an engine. Some 40 years ago the Cold Cranking Simulator (CCS) was developed to measure the low-temperature viscosity of engine oil with viscometric conditions similar to a starting engine. The importance of cranking viscosity has grown since the test was originally developed and is now one of two low-temperature viscosity measurements that define the SAE grades for engine oils. Previous studies evaluating viscosities determined by the CCS have focused on test precision and correlation to engine starting performance. This study evaluates the effects small offsets from the indicated temperature have on the measured apparent viscosity of engine oils. Interest in this topic was driven by the observation that some engine oil formulations have abnormally high variation in viscosity. All the low-temperature viscosity measurements were made in the CCS in accord with ASTM D 5293-04. A small temperature offset was achieved by adjusting the CCS temperature probe calibration so that the indicated test operating temperature was offset from the true temperature. The viscosity data were collected using automatic thermoelectrically cooled CCS instruments. Comparative viscosity data were collected on instruments using cold methanol to control the sample temperature. The oil samples in this study consisted of base oils, a selection of commercial engine oils of the API performance category SL, recent ASTM Interlaboratory Crosscheck Program (ILCP), and from the Low Temperature Engine Performance (LTEP) study which was conducted in the 1990s. The LTEP oils are of an earlier performance category and thus have a different composition than either the API SL commercial engine oils or the ASTM ILCP program oils. Results of this study show that when the CCS stator and sample are warmer than the indicated temperature, the measured viscosities are higher than when the viscosity is measured at the correct (true) temperature. As would be expected, the opposite response is seen when the offset is in the opposite direction. This response to the temperature offset is opposite of what would be traditionally expected—lower temperatures typically result in higher measured viscosities. As seen in the study, this is a result of the way the instrument is calibrated and not a fluid anomaly. Some of the API SL oils exhibited more than a 5 % change in measured viscosity from a 0.5°C shift in temperature. Base oils and synthetic formulations only had a change of around 1 % due to a 0.5°C shift in temperature. The samples of API SG oils have temperature sensitivity lower than the API SL oils tested. This study compares data obtained on instruments using two different methods of controlling sample temperature. For the samples evaluated in this program, the data indicated no relative bias between the two methods (thermoelectric and cold methanol) of stator temperature control.

An additive package of reconditioning functionality for worn ferrous surfaces has been designed in light of the mechanochemical reaction principle. The package is formulated from a fine-powdery multicomponent mixture of Serpentine minerals, surfactants, and catalysts. The main reconditioning component in the package is magnesium silicate hydroxide (Mg6(Si4O10)(OH)8), with the surfactants for dispersing the main component into bulk lubricant and the catalysts for facilitating interfacial mechanochemical reactions, particularly oil pyrolysis and carbonization. With commercial fully-formulated engine oils as benchmark, the reconditioning effects of the reconditioner package have been demonstrated in both laboratory tribotestings and in real-world heavy-duty (locomotive diesel engine) scenarios. Surface examination of sampled worn surfaces on both laboratory test specimens and cylinder bore of locomotive diesel engine has shown that a nano-crystalline layer has been generated which possesses nanometric roughness, higher surface hardness, and proper H/E ratio. Advanced analyses have indicated that the layer is composed of Fe3O4 and FeOOH nanoparticles which are dispersed on the Fe-C matrix. The smoother surface mitigates asperity interlocking which would otherwise induce high friction; the high surface hardness and appropriate H/E ratio result in less elastic deformation within nanocrystalline contact regions, which effectively lessens friction and wear arisen from plastic plowing and adhesion. Further characterization of sampled worn cylinder bore surface and analysis of used oils have suggested that generation of the nanocrystalline layer in presence of Mg6(Si4O10)(OH)8 involves three interwoven processes: oxidative mechanical polishing, lubricant carbonization and graphitization, and mechanical alloying.

To understand the benefits that tribological engineering materials or surface modifications provide, and ultimately to devise better ones, it is necessary to study the topographical, mechanical, physical, and chemical characteristics of surfaces. This paper reviews advanced surface analytical techniques for measuring surface topography and hardness of engineering surfaces. The primary emphases are on the use of these techniques as they relate to measurements of wear volume loss and nanohardness of materials using optical profilometry and nanoindentation in conjunction with atomic force microscopy, respectively.

Pitting is a form of fatigue failure which occurs on the flanks of highly loaded case carburized gears. The lubricants, consisting of base oil and additives, influence the pitting lifetime of the gear flanks. Common calculation methods of the pitting load capacity consider, along with the flank roughness and the tangential velocity, only the nominal viscosity of a lubricant as a lubrication relevant influence parameter. The actual lubricant performance and particularly the influence of the additives can be determined only experimentally. Within a FVA-research project a new “Practice Relevant Pitting Test” was developed to evaluate the influence of lubricants on the pitting load capacity of case carburized gears. The new test method is a mechanical test procedure which is based on the existing FVA-FZG-Pitting Test. It is defined as a single stage test which can be extended to an application test by testing the lubricant with a second load stage. In order to improve the practice relevance and to reduce the scatter of the test results the test uses superfinished test gears with adequate profile modifications. The extremely low flank roughness of the new test gears prevents particularly the appearance of undesired micro-pitting and therefore improves the reproducibility of the reached lifetime within the performed test runs. The new pitting test procedure was verified with different gear transmission lubricants and is seen as an improvement of the existing FVA-FZG-Pitting Test. It provides also a possibility to consider the test results for calculation of the pitting load capacity of industrial and automotive transmission gears with an additional factor ZLp which is to be applied in the calculation method according to DIN 3990. The paper describes the new developed test procedure “Practice Relevant Pitting Test” and discusses the correlation and classification to the existing FVA-FZG-Pitting Test.

The use of alternative base oils, like esters or polyglycols, with more intrinsic properties for the lubrication of automobile engines has a potential for ecological and technical advantages. Being in competition with hydrocarbon-based formulations, detailed knowledge of several thermophysical and viscometric properties as well as tribological properties over a large temperature range are required (mapping). The tested polymer-free polyglycols and ester-based formulations displayed no visible tribological weaknesses regarding wear resistance and EP-behavior as well as offering significant advantages in order to meet metal- and ash-free and bio-no-tox criteria. Especially the formulated polyglycols without friction modifiers also showed an intrinsic retention of low coefficients of friction and a hydrodynamic film forming behavior comparable to hydrocarbon-based factory-fill oils. The wear resistance and EP-behavior of low-additivated polyglycols, but also of esters, can be enhanced by means of triboactive materials. Lubricious oxides or triboactive materials and polar base oils, or a combination thereof, may substitute the EP and AW properties realized by the additives, thus enabling long drains and responding to “eco-tox” or “bio-no-tox” requirements as well as restrictions from the “chemical box.”

Oxidation resistance is one of the limiting factors for long drains, bionotox, LowSAP or NoSAP engine oils. The French iron catalyzed oxidation test (ICOT) uses 60 ppm iron acetylacetonate as diluted catalyst under an aeration of 10 L∕h at 170°C. The ICOT ranks the oxidation stability of oils according to three properties: a. the viscosity increase (e.g., max. Δη40°C

The U.S. Military specifies the use of Mil-PRF-2104 engine oil in the hydraulic system of certain nontactical military vehicles. Skid-steer loaders and other heavy equipment also use engine oils in their hydraulic systems. These vehicles are required to meet roll-off cleanliness specifications in order to improve hydraulic equipment reliability. Automatic particle counters are used to verify the cleanliness of these systems. Occasionally, particle counters detect phantom particles that cannot be removed by filtration. This paper examines the possible role of base oil and additive selection in the appearance of phantom counts. Filtered Group I and Group III base oils were doped with the components of an engine oil formulation. Particle levels were monitored before and after filtration using an on-line automatic particle counter. The results show that base oil selection has minimal bearing upon appearance of phantom counts while additive selection is a significant factor. Results from three different particle counters are compared. Two laser particle counters that operate by the light-blockage principle were found to produce phantom counts from polydimethylsiloxane antifoam additives. A direct-imaging laser particle counter classified antifoam particles as water droplets and was less susceptible to phantom particle interferences from silicone antifoam additives.

To meet the challenge of the increasing demand of fuel economy, in recent years low friction nonferrous coatings such as diamond-like carbon (DLC) coatings have become very popular for automotive tribo-components. The interaction of lubricant additives, which are designed for ferrous surfaces, with nonferrous coatings is an important issue for the automotive and lubricant industries. The aim of this paper is to establish a link between the evolution of antiwear zinc dialkyl dithiophosphate (ZDDP) tribofilm and the tribological performance of a DLC coating under boundary lubrication conditions. Experiments were performed in a pin-on-plate reciprocating tribotester to produce the tribofilm. Atomic force microscopy (AFM) was used to record high resolution topographical images of the ZDDP films while chemical analysis of the ZDDP tribofilms was performed using X-ray photoelectron spectroscopy (XPS). Results in this study show that the ZDDP tribofilm consists of short chain zinc pyrophosphate (Zn2P2O7) and zinc metaphosphate (ZnOP2O5), and it is formed along the raised portion of the initial marks of the DLC surface.

A review of current oxidation and deposit bench tests used for the evaluation of engine oil performance will be presented. Some of the more meaningful tests will be utilized to evaluate a number of antioxidant systems for oxidation and deposit control capabilities in engine oils formulated with 470 ppm of ZDDP-derived phosphorus. The antioxidant components are selected from a series of commonly used and commercially available materials plus one new developmental component. These components include an organo-molybdenum compound (MoDTC), an alkylated diphenylamine (NDPA), a conventional hindered phenolic (HPE), a high performance hindered phenolic (MBDTBP), and a new multi-functional boronated MBDTBP. The performance of these fully formulated engine oils will be ranked in the selected bench tests in order to highlight the benefits of each antioxidant system under evaluation. The results point to significant benefits with the molybdenum- and boronated-systems, or mixed molybdenum-/boronated-systems, for oxidation control, while systems containing NDPA and MBDTBP are favored more for deposit control. Unique and superior performing antioxidant systems will be recommended for screening in fired engine and bench wear tests.

A constant quest but a difficult goal is replacement of expensive and lengthy engine tests with more cost effective bench tests. This paper will report on development of a bench test, the ROBO, as a potential replacement for the Sequence IIIGA, an oxidative oil thickening engine test now part of ILSAC GF-4 specifications. Sequence IIIGA, a gasoline fueled engine running under severe conditions, is used to condition oils prior to determining TP-1 MRV viscosity, a cold temperature and low shear rate measurement. After Sequence IIIGA conditioning, candidate oils must meet SAE J300 pumpability limits at no more than 5°C warmer than its original SAE W grade. The ROBO bench procedure has been developed to potentially replace Sequence IIIGA engine aging by mimicking, to the degree possible, oxidative conditions found in the engine conditioning procedure. ROBO conditions were developed by employing the three Sequence IIIG ASTM matrix oils and comparing their used oil rheologies from multiple Sequence IIIG and ROBO runs. The results from the final ROBO conditions compare well not only for TP-1 MRV but also for KV 40°C and CCS. To further test the correlation of bench to engine conditioning, a set of diverse oils (various SAE viscosity grades and DI chemistries) have been examined; these viscometric data from ROBO and Sequence IIIG also compare favorably with only a few anomalies. Finally, the status of industry acceptance of ROBO will be discussed.