In this study, the effects of 15% methanol+85% gasoline blend (M15) on cold start HC emissions and performance of an spark ignition engine at idle and wide open throttle (WOT) conditions were investigated when using a thermal barrier layer (TBL) coated piston under various compression ratios (CRs). The performance tests were implemented at three CRs of 8.2, 7.2 and 6.2 for both standard ( STD) and TBL piston. When M15 blend was used in the engine with TBL piston at idle, cold start HC emissions decreased considerably at the CR of 7.2. Maximum decreases of 49.45, 47.05 and 32.2% in HC emissions of the engine with TBL piston at WOT were found at the CRs of 8.2, 7.2 and 6.2 respectively. It was observed that the brake power increased at all CRs without knocking, compared to that of the STD engine. Maximum increases of 5.8, 7.56 and 2.55% in the brake power were reached at the CRs of 6.2, 7.2 and 8.2 respectively. Specific fuel consumption of TBL piston engine was found 3.4% lower than that of the STD engine at the CR of 8.2.