"When a hydrocarbon fuel burns, some of the carbon gets deposited as a residue," T.R. said. "Builds up over time. My daddy used to take his Cadillac out on a long stretch of highway and put the pedal to the metal for a spell. Claimed he was blowing the carbon out of the cylinders. A routine maintenance procedure. Not sure if it really did anything but hoo-ee! It was a thrill to us kids in the back seat. Mom hated it. Anyway, an engineer would say this thing is getting coked up."