KNOB 1641153 - Caterpillar

Caterpillar Engines With Capsule-Type, Pencil-Type or 7000 Series Fuel Injection NozzlesFuel injection nozzles may incur damage when engines are severely overheated. This is especially true when a loss of engine coolant has occurred. Therefore, the fuel injection nozzles should be thoroughly inspected after an engine has severely overheated.
In most cases, a close inspection of the fuel injection nozzle will reveal evidence if the fuel injection nozzle has been overheated. Overheated capsule-type nozzles will typically have a bluish appearance. When a pencil-type fuel injection nozzle has been overheated, the carbon dam and plastic compression seal usually show evidence of melting. An overheated 7000 Series nozzle usually shows some discoloration and melting of the carbon dam. Analyzing Fuel Nozzles and Fuel Line Failures, Form SEBD0639, has additional information about inspecting fuel injection nozzles.
When a fuel injection nozzle is severely overheated, it may incur internal damage which could result in a future nozzle failure. If fuel injection nozzles show evidence of severe engine overheating conditions, all of the nozzles should be replaced.