Successful low-temperature operation of engines depends on the lubricant being able to flow to the oil pump. ASTM D5133, Standard Test Method for Low Temperature, Low Shear Rate, Viscosity/Temperature Dependence of Lubricating Oils Using a Temperature-Scanning Technique, is one of two tests the industry uses to assess whether the engine’s oil pump will be able to lift the lubricant from the sump at low temperatures. This test method requires several distinct steps to accomplish the required thermal conditioning. Accomplishing these steps in a consistent manner is necessary to minimize the variation in test results. Currently, ASTM D5133 has a repeatability of 16 % and a reproducibility of 29 %. This study demonstrates that automating the thermal conditioning steps yields better precision. Based on the samples tested, the automated procedure reduced the variability in test results by approximately 50 %. The data obtained show that the automated method provides a clearer distinction between lubricants whose flow properties were above the specification limit while having little impact on those at or below the specification limits. As a part of this study, the impact of small changes in shear rate was evaluated using the automatic procedure. Poor flow of lubricants at low temperatures can be due to the presence of wax crystals. ASTM D5133 uses a cylindrical rotor with a narrow gap between it and the stator, thus limiting crystal size. A portion of this study evaluates the impact of replacing the cylindrical rotor with a vane rotor. These measurements indicated that a vane rotor yields a stronger response for those samples with a test value greater than the specification limit but not those at or less than the limit.

The low-temperature viscosity of lubricants and hydraulic fluids is a key performance parameter in choosing an appropriate fluid. For gear oils, Automatic Transmission Fluids (ATF), and hydraulic fluids, ASTM D2983 is the primary test method for defining this low-temperature property. This article describes an approach to automatically measure this property for the aforementioned categories of products. It retains the critical aspects of D2983, which are the preheating, thermal conditioning from room temperature to test temperature, viscometer, rotor, and viscosity measurement criteria. Thermal conditioning follows that described in Annex 2 of D2983, and when complete, the viscosity is automatically measured. This requires a digital rotational viscometer with the capability to record viscosity and temperature as a key element in making the needed measurements. As described in D2983, viscosity measurements are made at discrete shear rate intervals (spindle speeds) for a set period of time. Upon the completion of a test, the data file contains a history of the thermal conditioning (time and temperature), plus the viscosity and torque at each spindle speed. By automating the procedure, the sample is undisturbed from the start of the test until the viscosity measurements begin. This eliminates errors due to sample preparation and temperature control throughout the test. Since the spindle is immersed in the sample throughout the test, the viscosity is measured on an undisturbed sample. All of this results in consistent thermal conditioning and a controlled temperature during viscosity measurement and eliminates operator-induced variance. Data on ASTM Proficiency Test Program samples and other commercial products indicate significant improvement in precision. The samples evaluated include ATF, automotive gear oils, and other products. An abbreviated procedure is described that could be suitable for some samples. This is achieved by shortening the soak time at the test temperature, but following the same thermal conditioning process prior to the soak at the test temperature.

This report describes the third CCM key comparison in capillary viscometry at twelve National Metrology Institutes (NMIs), which was carried out between October 2012 and February 2013. Seven NMIs, which do not maintain an independent viscosity scale, also took part in this comparison. Three samples of Newtonian liquids with nominal kinematic viscosities of 6 mm²/s at 15 °C and 5 mm²/s at 20 °C, 2000 mm²/s at 20 °C and 500 mm²/s at 40 °C, and 160000 mm²/s at 20 °C and 25000 mm²/s at 40 °C prepared by NMIJ were provided to each of the NMIs. For each of these liquids at two temperatures, total number of 98 measurements was carried out and from the results of viscosity measurements, the key comparison reference values (KCRVs) for six data sets were determined. The degrees of equivalences was evaluated by difference from the KCRV and, with a few exceptions, these differences were almost equal to or less than expanded uncertainties, showing a good equivalencies of capabilities at the participating NMIs for the viscosity measurements in wide range of viscosities covered from 5 mm²/s to 160000 mm²/s. KEY WORDS FOR SEARCH Main text To reach the main text of this paper, click on Final Report. Note that this text is that which appears in Appendix B of the BIPM key comparison database kcdb.bipm.org/. The final report has been peer-reviewed and approved for publication by the CCM, according to the provisions of the CIPM Mutual Recognition Arrangement (CIPM MRA).