It truly is a mystery to me, but my = long standing tick-tick- tick of a valve lifter is gone. The engine is a rebuilt = 2.1 with about 25k miles on it. Been run on Mobil 1 since about = 5k. Has had one noisy lifter since about 10k. Figured I'd be swapping it in the spring. Saw the Marvel Mystery Oil in a store over the weekend, = remembered seeing posts to the list about this stuff and figured (as they say in = Brooklyn) "it cain't hoit". Well, at the end of my first 15 minute drive...silence. I guess it's oil, it is a mystery, and it = sure is marvelous. Give it a try, it's a cheap experiment.