Dangerous to do if you slip and/or add too much water/seafoam while engine is running.
You can hydro-lock a cylinder, which WILL crack a piston or bend connecting rod, if too much liquid is added at one time, no "do-overs" for that
So steep downside on this "cleaning" method
But it does work to clean off carbon coating inside cylinders
Engine should be fully warmed up first
Your spark plug tips will tell you if you have carbon build up happening because they will get the same build up, also O2 sensors tips will show signs of carbon build up
This is from Rich air fuel mix and/or engine running at too low of a temperature so all the fuel is not burning, this leaves carbon behind.
And while cleaning it out is good you should then focus on the cause of it
If engine is only used for short trips, i.e. 5 to 10minutes at a time then it will often get carbon build up, also water vapor build up in valve cover area, underside of oil filler cap will have whitish residue.
A Cold engine must run Rich, Choke Mode, or it will stall, after 5 minutes or so air/fuel mix is leaned out, but it takes a while longer for engine to burn off that 5 minute build up
Driving 20-30 minutes once a week will usually keep engine cylinders clean, assuming there isn't a problem with air/fuel mix in general
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