Under high thermal load operation, engine oil consumption was monitored using the hydrogen fuel method. Burning was detected in the piston top-land clearance, and this may be a key to understanding the carbon adhesion mechanism on the piston top-land. The following results were obtained in this study: 1. Oil consumption is greatly affected by the evaporation of oil at temperatures higher than 160°C. 2. Burning is found in top-land clearances of hydrogen, gasoline, and large clearance diesel engines. However, only weak burning could be detected in diesel engines with tight-fitting crowns.