The metal parts Critical dimensions and surface finishes can change. A metal bellows can lose strength as the metal approaches its annealing temperature. Heat accelerates any corrosion problems caused by the product or any chemical used to clean the system. The product can change from a liquid to a solid or gas with higher temperatures. It can become more viscous.
Some products increase in viscosity as the become cold, others when they get hotter.
It can solidify. A change in temperature is enough. Some products solidify with heat, others with cold. A film can build on the hot seal surface restricting movement. This can occur at the lapped faces or in-between sliding components that must be free to flex and move.