I have seen this done on some older Honda, crazy lot of steam and smoke from the exhaust. It seemed quite aggressive method. Maybe OK for old cars.
I would be afraid about lambda sensors and clogging of the cats. And I would definitely be afraid to try it on the latest generation of diesel engines with EGR, cats, particle filters, heat exchanges, exhaust gas coolers, diesel missions Fluid/AdBlue injection.... And don't forget the carbon with steam leaves the engine through the hot part of the turbo, its small particles and steam might get to its shaft axis through the seals, scratch it and it would fail after few tenths thousands miles.
As zulu writes, using a good fuel and changing oil often is a better idea to keep the engine clean.
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