Hi all, when i went to the States about 2 years ago i was amazed by the number of repair shops using "sludge out" machines. These units connect to the engine via the sump and oil filter housings and re-circulate an additive which cleans the engine. A typical charge out is $120 with a material cost of about $30 and it takes only a few minutes to connect and about 15 mins to run the cycle.
Although i haven't yet purchased one of these machines, i do something similar using fuel flush additives. About 3 months ago we bought an immaculate condition Carbon Clean machine through an advert in the UK-Autotalk Workshop Trader for only £200 and it's paid back for itself at least tenfold. Instead of selling the customer a can of fuel flush, and perhaps making £5.00 profit, we now sell them a high pressure fuel injection cleaning service for £60 with a material cost of about £3.50 using Wynns Fuel System Purge.
Using this method definately transforms the way the engine performs, and i'm not just saying that as we have a dyno and "roll" almost everything.
Just remember, our customers can also go out and buy their own "mechanic in a tin" from any Partco or Halfords, what we in the trade need to do is dress it up a little differently.