12. Report
12.1 Apparent Viscosity and Yield Stress - For used oils, report the final test temperature and both apparent viscosity and yield stress.
12.2 Yield Stress - Report as less than the value at which rotation was observed.
12.3 Apparent Viscosity - Report as follows:
12.3.1 If the apparent viscosity is less than 5000 mPa·s (cP), then report the apparent viscosity as less than 5000 mPa·s (cP).
12.3.2 If the apparent viscosity is between 5000 and 100 000 mPa·s (cP), then report the apparent viscosity to the nearest 100 mPa·s (cP).
12.3.3 If the apparent viscosity is between 100 000 and 400 000 mPa·s (cP), then report the apparent viscosity to the nearest 1000 mPa·s (cP).
12.3.4 If the apparent viscosity is greater than 400 000 mPa·s (cP), then the apparent viscosity should be reported as greater than 400 000 mPa·s (cP).
12.3.5 When employing software that provides three viscosity values, the first value shall be reported as the apparent viscosity by this test method, D6896. If desired, report all three values, exercising care to also report the sequence of the values. Never report a value that is the average of the three measured values.
13. Precision and Bias
13.1 Precision (Used Diesel Engine Oils) - The precision of this test method as determined by the statistical examination of interlaboratory test results is as follows:
13.1.1 Yield Stress:
13.1.1.1 Repeatability - The difference between successive results obtained by the same operator with the same apparatus under constant operating conditions on identical test material would, in the long run, in the normal and correct operation of the test method, exceed the following values only in one case in twenty:
where:
X = mean value, Pa.
13.1.1.2 Reproducibility - The difference between two single and independent results obtained by different operators working in different laboratories on identical test material would, in the long run, exceed the following values only in one case in twenty.
where:
X = mean value, Pa.
NOTE 4 - When no yield stress is detected (movement with 10 g weight), X = 0.
13.1.2 Apparent Viscosity:
13.1.2.1 Repeatability - The difference between successive results obtained by the same operator with the same apparatus under constant operating conditions on identical test material would, in the long run, in the normal and correct operation of the test method, exceed the following values only in one case in twenty. The repeatability as a percent of the mean apparent viscosity is shown as follows:
13.1.2.2 Reproducibility - The difference between two single and independent results obtained by different operators working in different laboratories on identical test material would, in the long run, exceed the following values only in one case in twenty. The reproducibility as a percent of the mean apparent viscosity is shown as follows:
13.1.3 The interlaboratory program included six laboratories and seven test oils at the -20°C and -25°C test temperatures. The used oils included end-of-test drain samples from Mack T8, Mack T8E, Cummins M11-EGR and Mack T10 engine tests, with soot loadings (as measured by thermogravimetric analysis) ranging from approximately 5 to 9 %.
13.2 Bias - Since there is no accepted reference material suitable for determining the bias for this test method, no statement on bias is being made.
14. Keywords
14.1 low temperature flow properties; low temperature viscosity; mini-rotary viscometer; pumping viscosity; used diesel engine oil; viscosity; yield stress