When I was in college, one of the frat guys gave me a [car] ride to Chicago, along with 4 other guys - each one paid $10 to cover the gas for both trips there and back(!). It was in a 1959 Chevy 4-door sedan with the straight 6 (230 CID?) and over 300k miles on it. The day before the trip he changed the oil but used 4 cans of STP (8 ounces then) to make up the last quart. When he started up it stopped smoking after about 10 minutes: when we were on the return trip he gunned it down a freeway onramp and it made a Kawasaki 500 envious. When he saw it in his mirror he just said, "Well, there goes all the STP," and explained that if he hadn't done that run he could get 2000 miles before a quart of oil would be needed, but once that happened it would smoke all the way home - which it did: it used up 2 quarts of oil on the return trip - of 168 miles. Didn't leak a drop, though!