I have had a lot of experience with some of the 'Engine Flush' machines that are being used now, and most of them are so benign that they don't really do anything.
The first machine(s) we bought were the 'Bilstein R-2000(?)' machines. It hooks a hose to the oil filter adapter and one to the drain plug-hole. The machine holds 12 gallons of a 'proprietary' cleaning fluid, and with the engine off(static), it pumps 1 gallon into the car, and then circulates the entire 12 gallons through the engine,back and forth style(washing machine?).This goes for 10 minutes,then it drains and air-evacuates the engine, and repeats the whole process again. Whole service takes about 1/2 hour. During the cleaning,you can see the solution 'squirting' around the rockers and push-rods and all inside the valve covers. Each service uses a fresh 5-micron filter, and the machine gets a new 3-micron filter and 12 gallons of fresh fluiud every 40 flushes.
The kicker is that the filters are very easy to examine after the service is done, and even on the dirtiest, sludgiest engines we've flushed, there just doesn't seem to be much of anything on the filter. However, the engine does seem cleaner, based on the condition of the new oil put in afterward.
These machines are about $10K, and each service costs about $25 in product, so it is an expensive proposition.
About a year and a half ago, I put 9 Wynn's engine flush machines in some stores. Basically, they suck. They are dynamic(engine running) flush machines. All they really do is hook up a remote 5-micron oil filter to the vehicle and run the old oil with a quart of cleaning solution through for 10 minutes or so. When finished, air pressure blows it all out.
Both machines put on a good 'Dog and Pony' show, but the air flush at the end is really the only thing that gets the extra 'goop' out. It is not a service that I feel is worth the money, nor does it do anywhere near what the manufacturers claim it does. I no longer use engine flush machines in any of our locations. That cut out a lot of our potential sales, but I think it was the right thing to do.
I have also used the 'Envirolution' machine and many others, and they are all basically one of the two designs.
For many, many years, when I changed my own oil, I would always blow shop-air through the oil-fill before putting the drain-plug back in, and with the old filter still attached. It has always amazed me how much extra crud and sludge comes out this way. On my 460 Lincoln, I could get almost an entire quart extra of crud out!
When I have taken apart these engines, they are always exceptionally clean. It does a great job, and air is free!
