Got a buddy lookin at a boat with high hour mercury 575s as far as I know stock. Havnt got service records yet but they have 500 hrs. How are their lifespans.

With 500 hrs and if never opened up, it will be time for top ends at a minimum.

Surly they have been opened! I haven't heard of many making it past 200 hours without blowing the head gaskets lol.

right

What Quinlan said. If they have not been opened that is one high hour set of 575s. A few things about 575s, stock mapping sucks, fuel injectors are obsolete, low pressure lift pumps leak and take out sea pump bearings, flat tappet cams have been known to lose lobes, intakes rot out in salt water, blowers are not the most durable.

Unless it is a screamin deal on the boat (leaving enough $ for rebuilds) this would be one I would pass on.

Appreciate the input guys! I'll get some more details on them if they've had any work done. If not we will definitely move on. We were lookin mostly at 496 and 525 boats I just didn't know much about the 575s longevity I knew that had to be high

...and rockers and springs - ask me how I know. They are a good foundation for upping the HP though - I liked mine, but the fuel tanks on the 35' Lightning weren't big enough! LOL

I do have a good 575 fresh water intake for sale though!

I am in the middle of my 2nd rebuild. This time I caught it BEFORE it blowed up lol.

The first time Brad rebuilt, he punched mine out to 509s, aluminum heads, full roller, upgraded fuel system and several other new/ upgrades. Was pushing 750 hp. Now we just replaced the blowers w TBS swaps. That's when we found the current issues- luckily before I went and turned those new blowers ON!
Have been very happy.
they do like Fuel !!

As an experienced 575 boat owner, at 500 hours, the top end has been gone through at least once.
At 500 hours, you will need to at least do a good once over on the entire engines. Chances are the bottom end will need at least rings, the top end will need a complete go through and I would recommend making it a roller cam if it is not already. That will extend the life and let you gain some hp if you want. The blowers will need to be rebuilt and carefully check the intake manifolds as those have been a problem point for corrosion. Pressure test the headers as well.

Ron Potter built mine up to 700hp roller motors and they run like a champ!