I don't see the point in it. There are people here who drain all the oil, fill with diesel, gasoline, or a mixture and run it a few minutes. There are others who fill it with laundry detergent and water and run it a few minutes, then rinse with diesel. All say they have never had problems and that it helps extend the life of the engine to 100,000 km. They refuse to believe that an engine should last longer.
Just use a good oil in the first place. If you want it cleaner, change sooner. I took the valve covers off my gasoline 1988 BMW 325ic(200,000 km) and 1995 Diesel 4Runner a few weeks ago just to look. Both have been on a regular diet of Group I 20W-50 Diesel/Gasoline formula oils (books for both say 20W-50). The BMW gets changed twice a year, the 4Runner 6,000 km. Neither had sludge. BMW had a little carbon, probably because my wife drove home without water in it one day and cooked it.
4 days with a product like Auto Rx and the BMW lost all the noises that had become "normal", so I know there was varnish in the lifters that is no more. I'd rather use a product designed for getting the varnish out than a fuel.