Originally Posted by
Private jet
I remember these from JT9/RB211 days. Waste of time, made no difference.
That's certainly not what the engine companies would say.
I was at more than one engine company maintenance or "Working Together Team" conference where they reviewed the engine company recommended engine water wash procedures - along with potential 'got-ya's' to watch out for (fume events related to improperly done engine washes were not uncommon). The engine companies quoted a 5-10 deg EGT margin improvement for a water wash (depending on how dirty the engine was).
I also recall a few lively debates regarding what to use - plain water, filtered water, or various soaps.