What could occur if lead, zinc, or galvanized marks are created on an exhaust system?

When lead, zinc, or galvanized marks appear on an exhaust system, it indicates that the material is exposed to materials that can create a thermal or chemical reaction upon heating. These substances may not withstand high temperatures well and, as a result, could lead to the formation of cracks as the system heats and cools during operation. The difference in thermal expansion rates between the base metal and the markings can introduce stress, causing the material to crack.

While other factors such as clogging or corrosion are important considerations, they typically arise from different contributing factors within the exhaust system rather than directly from the presence of these specific marks. Decreased efficiency, while a potential consequence of exhaust issues, is more of an outcome of various problems such as blockages or leaks rather than a specific result of these markings. In summary, the interaction of these materials with the heat stresses present in an exhaust system is the primary reason for the formation of cracks.