ASTM D7110 Standard Test Method for Determining the Viscosity-Temperature Relationship of Used and Soot-Containing Engine Oils at Low Temperatures
1. Scope
1.1 This test method covers how to measure the apparent viscosity of used and soot-containing engine oils at low temperatures.

1.2 A shear rate of approximately 0.2 s(-1) is produced at shear stresses below 200 Pa. Apparent viscosity is measured continuously as the sample is cooled at a rate of 3 °C per hour over the range of -5 °C to -40 °C.

1.3 The measurements resulting from this test method are viscosity, the maximum rate of viscosity increase (Gelation Index) and the temperature at which the Gelation Index occurs.

1.4 Applicability to petroleum products other than engine oils has not been determined in preparing this test method.

1.5 The values stated in SI units are to be regarded as standard. No other units of measurement are included in this standard.

1.6 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.

2. Referenced Documents
2.1 ASTM Standards:
D341 Practice for Viscosity-Temperature Charts for Liquid Petroleum Products
D3829 Test Method for Predicting the Borderline Pumping Temperature of Engine Oil
D4684 Test Method for Determination of Yield Stress and Apparent Viscosity of Engine Oils at Low Temperature
D4057 Practice for Manual Sampling of Petroleum and Petroleum Products

3. Terminology
3.1 Definitions:
3.1.1 apparent viscosity, n - the viscosity obtained by use of this test method.
3.1.1.1 Discussion - See 3.1.7 for definition of viscosity and units.

3.1.2 digital contact thermometer (DCT), n - an electronic device consisting of a digital display and associated temperature sensing probe.
3.1.2.1 Discussion - This device consists of a temperature sensor connected to a measuring instrument; this instrument measures the temperature-dependent quantity of the sensor, computes the temperature from the measured quantity, and provides a digital output, or display of the temperature, or both. This device is sometimes referred to a digital thermometer.

3.1.3 Newtonian oil, n - an oil that, at a given temperature, exhibits a constant viscosity at all shear rates or shear stresses.

3.1.4 non-Newtonian oil, n - an oil that, at a given temperature, exhibits a viscosity that varies with shear stress or shear rate.

3.1.5 shear rate, n - velocity gradient perpendicular to the direction of flow.
3.1.5.1 Discussion - The SI unit for shear rate is the reciprocal second (1/s; also s(-1)).

3.1.6 shear stress, n - force per unit area in the direction of flow.
3.1.6.1 Discussion - The SI unit for shear stress is the pascal (Pa).

3.1.7 viscosity, n - that property of a fluid which resists flow.
3.1.7.1 Discussion - Viscosity is defined as the ratio of the applied shear stress (force causing flow) and the shear rate (resultant velocity of flow per unit distance from a stationary surface wet by the fluid). Mathematically expressed:
viscosity = shear stress/shear rate or, symbolically, η = τ/γ
in which the symbols in the second portion of Eq 1 are defined by 3.1.5 and 3.1.6. The SI unit for viscosity used herein is millipascal seconds (mPa·s).

3.2 Definitions of Terms Specific to This Standard:
3.2.1 air-binding oils, n - those engine oils whose borderline pumping temperatures are determined by a combination of gelation and viscous flow.

3.2.2 borderline pumping temperature, n - that temperature at which an engine oil may have such poor flow characteristics that the engine oil pump may not be capable of supplying sufficient lubricant to the engine.

3.2.3 calibration oil, n - Newtonian oils developed and used to calibrate the viscometer drive module over the viscosity range required for this test method.
3.2.3.1 Discussion - These calibration oils are specially blended to give sufficient sensitivity and range for the special viscometer head used.

3.2.4 computer-programmed automated analysis, n - use of techniques for acquiring analog data, converting these to digital values and using this information to automatically record and analyze torque output from the viscometer drive module and to render this information into tabular data and plotted relationships.
3.2.4.1 analog-to-digital (A-D) converter, n - a device for converting continuously produced electrical signals into discrete numerical values capable of being analyzed by computer technology.

3.2.5 critical pumpability temperature, n - the temperature at which an oil reaches a viscosity believed to be critical to limiting pumpability of the oil (see 3.2.6).

3.2.6 critical pumpability viscosity, n - that apparent viscosity believed to cause pumpability problems in an engine.

3.2.7 flow-limited oils, n - those oils whose borderline pumping temperatures are determined by viscous flow.

3.2.8 gelation, n - a rheological condition of an oil characterized by a marked increase in flow resistance over and above the normal exponential increase of viscosity with decreasing temperature, particularly at lower shear stresses and temperatures.
3.2.8.1 Discussion - Gelation has been attributed to a process of nucleation and crystallization of oil components and the consequent formation of a gel-like mass.

3.2.9 Gelation Index, n - the maximum value of the incremental ratio:
-[(log log η1) - (log log η2)]/(log T1 - log T2)
in which η is dynamic viscosity and T is temperature in Kelvin over the temperature range scanned when the incremental decrease in temperature is 1 K.
3.2.9.1 Discussion - The technique of deriving Gelation Index was first developed and practiced 4 by collecting information from a strip-chart recording and applying the empirical MacCoull-Walther-Wright equation. For further information, see Appendix 1 of Viscosity-Temperature Charts D341.

3.2.10 Gelation Index reference oils, n - non-Newtonian oils chosen to give certain levels of Gelation Index as a check on instrument performance.

3.2.11 Gelation Index Temperature, n - the temperature in degrees Celsius at which the Gelation Index occurs.

3.2.12 pre-treatment sample heating bath, n - a water or air bath to heat the samples for 1.5 h at 90 °C +/- 2 °C before testing.

3.2.13 programmable liquid cold bath, n - a liquid bath having a temperature controller capable of being programmed to run the calibration and the analysis portions of the test method.

3.2.14 temperature controller, n - a programmable device which, when properly programmed, ramps the temperature upward or downward at a chosen rate or series of steps while simultaneously controlling temperature excursions.
3.2.14.1 calibration program, n - a program to run the required series of temperatures at which the torque values necessary to calibrate the viscometer drive module are collected and analyzed.

3.2.14.2 test program, n - a program to run the test oil analysis at 3 °C/h temperature decrease.

3.2.14.3 hold program, n - a program to reach and hold the programmable liquid cold bath at -5 °C.

3.2.15 test cell, n - the combination of the rotor and stator. Critical elements of the test cell are sketched in Fig. 1.
3.2.15.1 rotor, n - a titanium rotor sized to give a compromise of sensitivity and range to the determination of viscosity and gelation using this test method.

3.2.15.2 stator, n - a precision-bore borosilicate glass tube, to which a measured amount of oil is added for the test and within which the specially-made rotor turns.
3.2.15.2.1 stator collar, n - a clamp for the stator which also positions it on the test cell alignment device.

3.2.15.3 test cell alignment device, n - a special device used to support the viscometer drive module while maintaining the stator and the rotor coaxial and vertical in regard to the viscometer driveshaft. Later designs admit dry gas into the cell to prevent moisture and frost buildup.

3.2.16 test oil, n - any oil for which apparent viscosity is to be determined using the procedure described by this test method.

3.2.17 viscometer drive module, n - the rotor drive and torque-sensing component of a rotational viscometer.

3.2.18 viscometer module support, n - a part of the test cell alignment device supporting the viscometer drive module.