Originally Posted by BogMonster
Further on this I was talking to the guy whose marina I am using at the moment, and he tells me he has never changed the impellers on either of his RIB engines (two 75hp Mariners, IIRC) since he got them new in 1995, never had any problems.
So perhaps they last better than I thought!
The problem is not so much how long they last (which is, like any mechanical piece, variable), but rather what will happen when it fails.
Losing the impeller means no cooling to the motor. No cooling causes an overheat, which, if not shut down in time, causes oil to thin, and adjacent moving metal parts to come in contact with each other. This causes wear and breakage, not to mention stranding you on the water, usually at the worst of times.
So, you end up with a tow back to port ($500 to a couple of thousand), a motor repair bill (couple of thousand minimum, I'd expect), and a few weeks off the water. The $100 or so to replace the impeller is pretty cheap insurance, all things considered.