FED-STD-791D
Method 203.1
September 30, 1986
POUR STABILITY OF LUBRICATING OILS
1. SCOPE
1.1 The test for pour stability is primarily intended for use with engine lubrication oils.
However, by establishing proper final cooling temperatures, this method can be used for other
lubricating oils such as power transmission fluids and hydraulic oils.
1.2 Good correlation with field test results has been obtained. However, since only two
temperature/time cycles are reproduced, this method cannot duplicate all field ambient cycle
conditions.
2. SUMMARY
2.1 After preliminary warming, the sample is subjected to a controlled temperature/time
cycle over 5-1/2 to 7 days. Two cycles have been established to reproduce pour instability or
reversion which has occurred during storage of oils in moderately cold cyclic ambient
conditions. Oils exhibiting pour reversion are essentially "solid", resulting from wax gel
formation, at temperatures significantly above their ASTM D 97 pour points.
3. SAMPLE SIZE
3.1 Approximately 100 mL of test lubricant.
4. REFERENCES, STANDARDS, AND APPARATUS
4.1 Test Jar - Identical to ASTM D 97 and D 2500 pour point/cloud point test jar.
4.2 Thermometer - ASTM E-1 6C with temperature range of +20 to -80C.
4.3 Cork - to fit test jar.
4.4 Heating bath - hot water to precondition test samples (80C).
4.5 Cooling bath - low temperature with controller to follow temperature/time cycles
from +15C to -45C. Spacing between test jars is to be about 1.5 cm with jars suspended so that
cooling medium circulates around bottom and sides of jars.
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