PURPOSE: To obtain a heat insulating layer for preventing a combustion chamber from being super-cooled, by charging a mixture liquid in which a solvent and metal particles are added in heat resistant resin, into a cooling passage, by turning an engine to coat the mixture liquid on the wall surface of the cooling passage, and thereafter by baking the same.

CONSTITUTION: A mixture liquid in which aluminum powder corresponding to a cooling ability required for the wall of a cooling passage 5 in an engine is added in heat-resistant epoxy resin, is prepared, and is charged into the cooling passage in the engine. Thereafter, the engine body is turned or swung to coat the mixture liquid on the wall surface of the cooling passage 5. Thereafter, the thus obtained coating layer is baked to remove the solvent thereof, to complete a heat insulating layer 6 made of epoxy resin containing scale-like aluminum powder.