Mercruiser I/O life expectancy
 

I’m new to the form. Previously I’ve purchased a few Formulas a number of years ago with I/O power. I previously owned a 1999 400 SS with 502 mag MPI’s that I purchased new so I do t have any experience purchasing a used boat with I/O power. I’m now looking to purchase a used 400 SS. The boats I’m looking at are equipped with 496Mag or 500 HP engines. I’m looking to see what major services need to be performed on these engines when the hours build up. Some of the boats I’m looking at have 400 to 500 hours. Is there a number of hours that these engines may need to be rebuilt? How about the outdrives. Is there a general guideline where they need to be rebuilt or replaced and what services should I look for that should have been performed on the engines and outdrives? Thanks

That's a heavy boat for Bravo drives.
with HP500 motors in that heavy boat, it is asking a lot out of the drives. 500 hours would (my guess) be pushing the lifespan of a drive - most likely it has already killed a pair of drives by that point.

Engine-wise an HP500 will need valvesprings around 250 hours.