FASTENER 5W3695 - Caterpillar

the catalyst substrate for discoloration, buildup of foreign deposits and uniform coating on the surface of the substrateA tan, or light brown to dark brown discoloration of the catalyst substrate may occur from normal operation. A small amount of gray and white ash may occur from normal operation. If either of these conditions occur, but the exhaust system back pressure is normal, and the temperature differential across the converter is between 0°C (32°F) and 40°C (72°F), no corrective action is required.If any of the following are observed, refer to System Operation, Troubleshooting, Testing and Adjusting, KENR6870, "Catalytic Converter Substrate - Inspect" for the proper corrective action:
soft black sooty deposits on the substrate
carbon fouling of the substrate
large amounts of powdery gray and white ash covering the substrate
dark bronze or black color on the substrate
white powdery appearance