ASTM D7110 Standard Test Method for Determining the Viscosity-Temperature Relationship of Used and Soot-Containing Engine Oils at Low Temperatures
8. Sampling
8.1 Approximately a 20 mL sample of test oil is necessary for the test. The sample must be thoroughly shaken so that the sample is homogeneous (see 12.1).

NOTE 2 - The submitter of samples should refer to Practice D4057 to be aware of how to properly acquire representative samples of petroleum products.

9. Preparation of Apparatus
9.1 Pre-treatment heating of samples using either a water bath or an oven.
9.1.1 Water Baths - Using boiling distilled water and correcting for barometric pressure (if significant because of altitude of the laboratory), check the calibration of liquid-in-glass or digital contact thermometer used in the pre-treatment water bath by appropriate methods.
9.1.1.1 Check the constant temperature of the pre-treatment water bath after ensuring that it is filled with distilled water to a level 20 mm above the oil level in the immersed stators. The temperature should be constant at 90 °C +/- 2 °C.

9.1.2 Ovens - Check the calibration ofthe temperature sensing device by appropriate methods. The temperature should be constant at 90 °C +/- 2 °C.
9.1.2.1 Determine the length of time required to bring the sample up to 90 °C. Use this time interval to establish the length of time the sample is held in the oven before being poured into the stator.

9.2 Preparing Liquid Cold-bath - Check the liquid level in the programmable liquid cold bath. Fill bath to proper depth according to supplier's instructions at -5 °C.

NOTE 3 - To ensure adequate cooling fluid height above the sample, it is advisable to fill the bath at -5 °C to the appropriate level indicated by the manufacturer and to always bring the bath back to this temperature when on stand-by. This keeps down the evaporation rate. In addition, for many refrigerating baths, operation at some temperature moderately below room temperature maintains best operational response. Coolant should not be added to the bath while at lower temperatures to avoid overflow at room temperature as well as disruption of the cooling cycle.

9.2.1 Install or check the cooling programs for the programmable liquid cold bath. The programs to be implemented are shown in Table 1 and Table 2.

9.3 Determine that the upper hook threaded (left hand thread) to the viscometer drive module's driveshaft is firmly finger-tightened. In the tightening process, gently and slightly lift the driveshaft.

NOTE 4 - Do not pull down or push or pull laterally on the driveshaft as this may harm the internal jeweled bearing and perhaps bend the driveshaft as well.

10. Preparation for Calibration of Cells and Testing of Samples
10.1 Programmable, Liquid-coolant, Cold Bath:
10.1.1 Check water content of methanol bath coolant every one to six months, depending on average ambient humidity levels. Water content should be less than 6 %. If not, replace bath coolant with fresh (<0.5 % water content) methanol.

10.1.2 Fill bath to proper level with fresh (<0.5 % water content) methanol coolant. Methanol coolant level in the bath should be a minimum of 15 mm above oil level in stator at lowest temperatures of analysis (see Fig. 1).

NOTE 5 - The low-level indicator light is illuminated on the bath when the coolant level falls below 35 mm above the oil level in the stator.

10.1.3 Using the liquid bath temperature controller and manufacturer's instructions, temporarily set bath temperature at -20 °C and allow to come to equilibrium for 1 h. Check bath temperature using an accurate and sensitive temperature indicator such as a short-range, partial-immersion thermometer or other thermometric device. If the temperature indicator shows that the bath temperature is more than +/- 0.2 °C from set point on the bath thermoregulator, follow the bath manufacturer's instructions to readjust the control setting on bath thermoregulator to align bath temperature with temperature indicator.

NOTE 6 - Accuracy of the temperature indicator should be checked against a distilled water ice-bath to determine any necessary temperature correction.

10.1.4 Follow the bath manufacturer's directions for using the thermocontroller for calibration and test programmed settings.

10.1.5 Set the bath to hold at -5 °C until either a calibration or test program is started.

10.2 Clean and prepare test cell rotors, rotor hook connectors, and stators.
10.2.1 Clean and dry test cell rotors and stators of any residues of oil from previous tests using suitable techniques before reusing.

10.2.2 Attach left-hand threaded rotor hook to rotor shaft connector by firmly finger-tightening the hook to the rotor to seat the connection.
10.2.2.1 Check the rotor shafts and connected hooks for straightness as directed by the manufacturer.

10.2.3 Attach left-hand threaded viscometer hook to viscometer drive-shaft connector (see Fig. 1) carefully. Exercise particular care that the viscometer drive-shaft connector is lifted slightly during hook connection so that no damage occurs to the jeweled pivot bearing within the viscometer head.
10.2.3.1 Check straightness of the viscometer head hook shank by running viscometer at 12 r/min and observing any shank oscillation. If oscillation occurs, the hook must be replaced. If oscillation is in the viscometer drive and not in the hook, the viscometer head must be repaired or replaced.

10.3 Set up oven or hot-water heating bath for preheating the sample at a temperature at 90 °C +/- 2 °C.

NOTE 7 - Direct heating of the oil on a hot plate is not recommended for this purpose because of the adverse effects of a localized heat source on the oil and the greater difficulty in controlling bath temperature excursions. However, indirect heating of the oil samples using a temperature-controlled water bath heated by a hot plate is acceptable as long as the samples are covered to protect them from water vapor.

10.4 Turn on dry gas supply and set each gas line to deliver approximately 10 mL/min to 20 mL/min. to each cell.

11. Calibration of the Test Cell
11.1 Computer Method:
11.1.1 Set up cell and viscometer head as directed by the manufacturer using a reference Newtonian oil having an appropriate viscosity range and established as a standard for this test method.

11.1.2 Select special calibration cooling program shown in Table 1 on programmable liquid cooling bath according to bath manufacturer's instructions, but do not start the program.

11.1.3 Open and enter required viscosity and temperature data in computer program.

11.1.4 Open main flow control valve for dry gas flow above liquid in stator at approximate rate of 10 mL/min. per cell.

11.1.5 Simultaneously initiate:
11.1.5.1 Cooling program on cold-bath, and

11.1.5.2 Data recording on computer according to bath manufacturer's instructions.

11.1.6 Collect and analyze complete recorded data using program developer's instructions.

11.1.7 The correlation coefficient, R, should be R ≥ 0.999. If not, another calibration run should be made to check the results and if no improvement is shown, the equipment manufacturer should be contacted for advice.

11.1.8 The viscosity intercept should be within manufacturer's limits. If it is not, the equipment manufacturer should be contacted for advice.

12. Preparation for Analysis of the Test Oil
12.1 Homogenize the sample in its original container thoroughly by stirring, shaking, or rolling, depending on the container geometry.

12.2 Pour the test oil into the stator to the fill line on the stator (see Fig. 1) in preparation for preheating and cover with a latex finger cot to prevent any loss of more volatile components or condensation of moisture.

NOTE 8 - A beaker may be used to preheat the test oil in an oven or in a water bath (if covered to prevent volatilization of components or condensation of moisture). In all cases, however, preheated oils are to be poured into their respective stators within a few minutes after completing the preheating step.

12.2.1 Place samples in preheating device at 90 °C +/- 2 °C and hold for 90 min to 120 min.

12.2.2 Remove the samples from the heating device, exercising care in handling the hot equipment and samples. Remove the finger cots at this time. Proceed immediately to 12.3.

12.3 Allow no longer than 15 min for samples to cool sufficiently to allow handling.
12.3.1 At a sufficient angle to prevent trapping bubbles on the flat rotor bottom, insert matching, room-temperature rotor into the appropriate stator in preparation for joining the test cell to the adapter/viscometer head support and proceed immediately to 13.4 for continued preparation and cold-bath immersion.

NOTE 9 - Heating the rotor with the stator and test oil prolongs cooling considerably and is not acceptable for this test method.