I have flipped them ONLY to check the function of the pump in a tank if I was waiting for a new impeller to arrive. Flipping them over is a bad idea and should never be done if the motor is being run on a boat. It accelerates the process of the vanes breaking off just as been mentioned here above. Once you spend hours, days, weeks, or more getting pieces out of the cooling system when one disintegrates, that will be the last time you flip one… even if you are lucky enough to catch it before you roast the powerhead. Definitely not worth it.
Then last one I had apart for about 6 weeks getting all the giblets out of the works. That one had either been flipped by someone else or just run to complete failure. A brand new impeller was used and still no water to the powerhead, so I had to get after the pieces. What a pain. 😥
Looks like I don’t have the picture of that one anymore but I have a couple others of failed impellers.
-Ben
OldJohnnyRude on YouTube