EXPLANATION
This test method covers the determination of pentane and toluene insolubles in used lubricating oils. Pentane insolubles can include oil-insoluble materials and some oil-insoluble resinous matter originating from oil or additive degradation, or both. Toluene insolubles can come from external contamination, fuel carbon, and highly carbonized materials from degradation of fuel, oil, and additives, or engine wear and corrosion materials. A significant change in pentane or toluene insolubles and insoluble resins indicates a change in oil which could lead to lubrication statem problems. The insolubles measured can also assist in evaluating the performance characteristics of a used oil or in determining the cause of equipment failure.
TEST SUMMARY
There are two test methods used. Procedure A covers the determination of insolubles without the use of coagulant in the pentane. It provides an indication of the materials that can be readily separated from the oil-solvent mixture by centrifugation. Procedure B covers the determination of insolubles in oils containing detergents, and employs a coagulant. In addition to the materials separated by using Procedure A, this coagulation procedure separates some finely divided materials that may be suspended in the oil.
The results obtained by Procedures A and B should not be compared since they usually give different values. The same procedure should be applied when comparing results obtained periodically on an oil in use, or when comparing results determined in different laboratories.
In Procedure A, a sample is mixed with pentane and centrifuged. The oil solution is decanted, and the precipitate washed twice with pentane, dried, and weighed. For toluene insolubles a separate sample of the oil is mixed with pentane and centrifuged. The precipitate is washed twice with pentane, once with toluene-alcohol solution, and once with toluene. The insoluble material is then dried and weighed. In Procedure B, Procedure A is followed except that instead of pentane, a pentane-coagulant solution is used.
TEST PRECISION
Where X is toluene insolubles or coagulated toluene insolubles.
The reproducibility of this test is so poor that Procedure B coagulated toluene insolubles is unsuitable for comparing interlaboratory results.
This test method has no bias.