The test duration of the each experiment is fixed based on the microstructure investigation and until the WEA formation is observed in the sample. The summery of test results of three lubricants is given in Table 1. Metallographic inspection of the samples tested in three different oil is illustrated in Figure 1. Several irregular shaped WEA formations observed in mineral oil sample is shown in Figure 1 (a). Long linear cementite formation in PAO sample shown in Figure 1(b) indicate the precursor of long WEA formation in samples. Similarly, one butterfly shaped WEA formation observed in PAG sample is shown in Figure 1 (c). © STLE 2019 - 74th Annual Meeting and Exhibition of the Society of Tribologists and Lubrication Engineers. All rights reserved.