My mechanic used Marv. Mystery Oil as well for '86 GT Coupe. In hotter climes, my coupe would make a lot of racket. I would actually add a little Marv. Myst. while the car was running and it would quiet down. Pretty amazing. PS-been told it is NOT advisable to add Marv. Myst to gas tank-though the label says it's ok. Also, don't add it to the oil if you don't already have problems.