It's unlikely that you will do any damage to your M3 by putting Seafoam into the engine, but it's just as unlikely that you will see any real benefits either. Snake oil salesmen love to talk about "carbon deposits", but those haven't been an issue in automobiles since metered fuel injection replaced carburetors and all fuels were given added detergents. Carbon deposits are a result of overly rich mixtures and incomplete combustion, and if you have either your SES light will be lit like a Christmas tree. This is the same reason that the so-called "Italian tune up" is an anachronism. Hey, if it makes you feel better, go ahead and do it, but if you have any real carbon deposits in the innards of your engine you have some problems that urgently need to be addressed.
Last edited by DSilk56; 09-07-2012 at 02:44 PM.