TEOSTThermo-Oxidation Engine Oil Simulation Test (high-temperature oil evaluation)
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In addition, correlation between the GMTC engine test and the TEOST 33C bench test, as well as an assessment of the relationship between engine oil field turbocharger deposits and TEOST 33C deposits will be discussed.
Mo components have long been implicated in an increase in turbocharger deposits as measured by the TEOST 33C bench test [17].
Molybdenum based organometallic components, such as molybdenum dithiocarbamate (MoDTC), typically show a significant increase in total deposits as measured in the TEOST 33C bench test with increasing Mo content [17].
However, it performed poorly in the TEOST 33C test, with total deposits of 51.5 mg (see Figure 8).
Both the GMTC engine test and TEOST 33C bench test were designed to evaluate an engine oil's propensity to protect a turbocharger from developing harmful deposits.
As an additional comparison of the GMTC test to the TEOST 33C test, end of test average turbocharger merit ratings for tests that completed 2000 cycles (not a pass fail parameter) were compared to TEOST 33C test total deposits (Figure 9).
As mentioned earlier lubricants with high Mo content such as Oil E in Q4 in Figure 8, performed significantly better in the GMTC test than in the TEOST 33C test based on current pass/fail criteria.
This may be the main reason that many oils in Q4 of Figure 8 performed well in GMTC test, but not the TEOST 33C test.
Figure 10 illustrates that these two different Mo containing oils generated very different levels of TEOST 33C deposits.
The results support the observation that there is no relationship between gasoline turbocharger cleanliness performance in a vehicle and deposit tendency in the TEOST 33C test.
No correlation between the GMTC test response, measured as the percent increase in TCO temperature or average turbocharger deposit merit rating, and total deposits measured in TEOST 33C was observed.
Passing and failing TEOST 33C oils resulted in no significant difference in engine sludge and turbocharger deposit ratings in gasoline turbocharged vehicles under field driving conditions.