EVALUATION OF HIGH-TEMPERATURE LIQUID LUBRICANTS USING THE PENN-STATEMICRO-OXIDATION TEST

High-temperature liquid lubricants are being developed for advanced di esel engines. Bench testing of lubricants is crucial to the success of this program. The Penn State micro-oxidation (PSMO) test has shown go od correlation with ASTM III-D sequence engine tests and with heavy-du ty diesel engine tests. In this study, the PSMO test was used to evalu ate a commercial mineral oil-based diesel engine lubricant and two exp erimental synthetic formulations for their deposit forming tendency an d their thermo-oxidative stability under thin film conditions. A compl ex series parallel reaction network appears to determine the terminal deposit level. The effect of base oil oxidative and thermal stability on the deposit forming tendency has been discussed. PSMO tests coupled with gel permeation chromatography (GPC) were used to study the pathw ays leading to the oxidative degradation process and to Provide possib le reasons for viscosity increase exhibited in the crankcase during en gine testing. The temperature range covered in this study is typical o f the temperatures anticipated for future high-temperature diesel engi nes.