Perhaps you could add here that, due to a recent discussion, it has been proven that engine flushes of all kinds being sold and other bootleg flushes such as diesel, while being harmless to an engine when used as directed, do not, in fact, create much of a benefit to either justify the cost or the added time required to do the flush.
This is because :
1. If you run brand name fully synthetic oil, and
2. Change your oil and filter at the recommended intervals.
...no matter how high the mileage of the engine, it will be mostly free of sludge. What little that is left is is too little to make a difference to either the engine's internals or its performance, when it is removed by a flushing solvent.
Perhaps the only time when it is worthwhile to flush an engine would be at your first service interval after you've bought that car, since you don't want to assume that the po (previous owner) has been changing the oil whenever he should and has been using premium brands such as LiquiMoly and Mobil1. when he held onto the car. Thereafter, there would be no need, assuming of course that you're going to do your part henceforth.