Hi, never, as far as I have seen And I run it in all of my mercs (13) . I have pulled heads from engines I have run it in and everything has been perfectly clean with no carbon in the combustion chambers. One thing I have learned though is the Aston martin DBS V8 owners are cautioned against using many of the octane boosters' sold by auto shops because it builds up on the intake valve stems and this build up causes valves to stick . I have never seen this in Engines running ATF.