Characterization of TEOST Deposits and Comparison to Deposits Formed on Sequence IIIG Pistons

In the next ILSAC passenger car motor oil specification the Sequence IIIG engine test, as well as two versions of the Thermo-Oxidation Engine Oil Simulation Test (TEOST) have been proposed as tests to determine the ability of crankcase oils to control engine deposits. The Sequence IIIG engine test and the TEOST MHT test are designed to assess the ability of lubricants to control piston deposits and the TEOST 33 test is designed to assess the ability of lubricants to control turbocharger deposits. We have previously characterized the chemical composition of Sequence IIIG piston deposits using thermogravimetric, infrared and SEM/EDS analyses. Sequence IIIG piston deposits contain a significant amount of carbonaceous material and the carbonaceous material is more prevalent on sections of the pistons that should encounter higher temperatures. Furthermore, the carbonaceous material appears to be a deposit formed by the Sequence IIIG fuel. In the TEOST tests no fuel is present, but the base oils used to formulate engine oils are a possible source for carbonaceous deposits. In addition, the TEOST 33 operates at higher temperatures than the TEOST MHT. Our current research involves characterizing TEOST deposits using the techniques previously employed to characterize Sequence IIIG piston deposits. The composition of the TEOST deposits and Sequence IIIG piston deposits are compared and the effect of temperature on the composition of the deposits is discussed. Finally, the relationship between base oil structure and TEOST deposit formation is discussed.