so, is anyone that's posted actually an engine rebuilder or qualified mechanic? Reason being, it was actually a mechanic from a well known and respected tuning workshop that recommended this as a way of removing carbon deposits from an engine we were having trouble with (and no, he did not have a spare engine there he was trying to sell). It is putting water through an engine so I'm not surprised about some of the comments lol, but I have seen it work firsthand and done it several times in different engines, and never had any engine trouble afterwards, no water in oil, nothing. Small amounts being the key, not a gardenhose or firehose, although I admire the enthusiasm there