[djb383]

Seafoam, when added directly to the intake, will belch white smoke whether the engine is brand new or has 250,000 miles on it. It's an oil based product and can momentarily/temporarily foul plugs, when added to the intake too quickly, which will trigger a CEL because the system detects a cylinder misfire. If you add it to the gas tank, you won't have the plug foul problem. Also, the only way Seafoam will clean the injectors, is to add it to the fuel tank. Adding it directly to the intake just bypasses the injectors. As lean as these trucks run (ULEV II) there's no way you have cylinder carbon build up at 20K miles. Again, it will smoke in a new engine just as much as in an old engine.