To provide a method of estimating a thermal history of a resin product or a rubber product in an automobile engine room, without finding " a relational expression between the thermal history and a physical property" or " a relational expression between the thermal history and a DSC heat absorption peak temperature", in every of the products different in materials, and further without imparting a damage onto the product for history evaluation.

A prescribed size of indicator prepared by a crystalline resin having a melting point of 150°C or more is bonded to the resin product or the rubber product installed in the engine room, and is recovered/sampled after a prescribed lapse time to estimate the thermal history, based on DSC analysis.