PISTON DEPOSITS BY TEOST MHT: ASTM D7097
EXPLANATION
This test method is designed to predict the deposit-forming tendencies of engine oils in the piston ring belt and upper piston crown area. Correlation has been shown between the TEOST MHT procedure and the TU3MH Peugot engine test in deposit formation. Such deposits formed in the ring belt area of a reciprocating engine piston can cause problems with engine operation and longevity. It is one of the required test methods in Specification ASTM D4485 to define API Category Identified engine oils. This test method covers the procedure to determine the mass of deposit formed on a specially constructed test rod exposed to repetitive passage of 8.5 g of engine oil over the rod in a thin film under oxidative and catalytic conditions at 285° C. The range of applicability of the Moderately High Temperature Thermo-Oxidation Engine Test (TEOST MHT) test method as derived from an interlaboratory study is approximately 10 to 100 mg. However, experience indicates that deposit values from 1 - 150 mg or greater may be obtained. This test method uses a patented instrument, method and patented, numbered, and registered depositor rods traceable to the manufacturer, and made specially for the practice and precision of the test method.
TEST SUMMARY
Deposit-forming tendencies of an engine oil under oxidative conditions are determined by calculating an oil-catalyst mixture comprising a small sample (8.4 g) of the oil and a very small (0.1 g) amount of an organo-metallic catalyst. This sample mixture is then circulated for exactly 24 hours in the TEOST MHT instrument over a special wire-wound depositor rod heated by electrical current to a controlled temperature of 285° C at the hottest location on the rod. The depositor rod is weighed before and after the test, and any deposit formation on the rod as well as any deposits collected from rod washings are determined. During the test, precisely controlled and directed air is caused to bath the oil flowing down the depositor rod and, thereby, to provide opportunity for oxidation. Precision of this test is strongly influenced by care in manufacture of the wire-wound steel depositor rods and the treatment of the coating of the wound wire, the rate of air flow, and the amount and degree of mixing of the catalyst.
TEST PRECISION
Repeatability: 0.15(x + 16)
Reproducibility: 0.35(x + 16)
Where x is the mean of two test results.
No information on the bias of this method can be presented because no material having an accepted reference value is available.
