FAA request for info

Not sure on the temp the powdercoaters use but its up towards 300 degrees or over. You would have to call Advanced PC to see what they use. I do know that if you have to re-coat sealed struts they smoke like crazy as the oil burns off inside (if you drill them to vent of course).

The rudders are definitely not oiled inside. All steel tubing comes from the manufacturer with a certain amount of oil on it to keep from rusting in transit and it normally stays there outside of welded areas. That could be the black residue referred to.