ATF has a copious amount of detergents in the oil. I've had cars come in to the shop, horrible maintenance, stuck variable valve time units due to crud build up, and ill run a quart of ATF thru with the oil for about 500 miles and the shit that comes out in the drain oil is amazing. it'll get into little areas and bust stuff loose. now, this is not always a good thing. but it cleans like a son of a bitch.