Well I decided to try some Kreen in my 160k-mile 2007 Tahoe. The first owner (who had it the first 120k miles) took good care of the car but the second owner.. not so much. The car was burning about 1 quart of oil every 3k miles (very common with the 5.3L and no big inconvenience), but the real problem was the visible oil burning every cold start - it was pretty embarrassing. Well only 250 miles into my Kreen experience, there is no longer any smoke at startup. None. The car idles a little smoother (there wasn't much to improve on there), and my mpg is up from 14.4 to 15.5 (with no other changes). Honestly I'm a big skeptic of these "tune up in a bottle" type cleaners since I've tried so many with no changes. Kreen seems to have done some good here, and I can still smell it burning so I can only hope there's more to come. I am tempted to try it in my 2007 E63 but that M156 engine runs so clean and has so many sensors that I can only see bad things coming of it!