I have a stock 502 efi motor in my 93 formula with around 600 hours on it. Just wondering how long these magnums usually last. Its never been beat on or tweaked, all stock. As far as i can tell also never been beat on too hard. just wondering how many hours i should get out of this thing and still have it be dependeable and when it requires a rebuild. Thanks for your help

how is your compression, leak down test, oil pressure? these are the things to look at, 600hrs is alot of time.

It all depends on how the motor was cared for and how it is used.

If it was mine, at 600 hrs I would do a compression and leakdown test to at least give me an idea of the current health of the motor. Also check the hot oil pressure at idle. If it is low, then the bearings are worn out.

All in all, if the boat runs good and you are happy, keep maintaining it and have fun !!!!

I have 500 hrs on mine and they still perform as well when I got the boat with low 200 hour range on them.They are all stock and well maintained.
I have been told 800 to 1000 hours is not uncommon by Mercury techs and people with that many hours already on them. Of course use and maintenance plays a role in there life. I would say change your oil every 30 hours or so, don't run it hard till the engines are fully warmed up, and keep an eye on/replace your exhaust riser gaskets.

Back when I used to own my Parasail business and we would run the 330hp 454 in the Nordic parasail boats we would get 2500 to 4000 hours out of a motor. Than we would replace them not because they were bad but they had served their time and we could afford to throw in a new one.They all ran a PTO off the crank that would cycle off and on thousands of times over a lifespan and the motors were ran in the 3500 to 4000 range quite a bit with some long wide open runs for whole days if the wind was light.

The last gas boat we had i pulled the old 4000 hour motor out and threw in a brand new motor and drive package before spring break season started.Had nothing but problems with it and it spun a main after 40 hours. Threw the old motor back in while i waited for Merc to replace it and it never missed a beat.
Than we switched to the Volvo Dieasels and learned you only got about a 1000hours out of them before they were so far down on compression that they only had 2/3 the power and would have to be rebuilt.

The Yanmar 315s were losing compression and power at 2500 to 3000 hours.

Worst thing you can do to a motor is overheat it. Keep a fresh impeller in it and turn it off if the temp ever starts climbing and they last forever.
Replace the risers and manifolds every 3 years if you are running in saltwater and the blocks are good for 6 years if you are not flushing them.

one of my customers has 1200 + on his and still runs like a watch..

I have seemed to notice a lot of performance boaters seem to worry about rebuilding stock or Magnum engines before there time me included. I know of a few cruisers with gas powered big block Chevys going 1600 plus hours with out rebuild and those cruisers have to be putting more load on the engines by pushing more weight and beam thru the water than your typical sport boat. Is it by nature that us performance boaters are that much more anal about maintenance and improving things that we do stuff before it's time or are Magnum type Merc Engines that much less reliable than standard 300-350 H.P. bib blocks? Does running a higher R.P.M. range with less resistance in a offshore harder on an engine than less R.P.M. in a heavy wider cruiser under more load?

I friend of mine checkmate has 800hours on the 502 so far, still runs good

I would expect top end refresh's in the 500-700hr range and full rebuilds in the 1000-1400hr range.

Thanks for all the replies guys. Its nice to know that some of you get 1000's of hours out of these motors. And as always i maintain it 100%. I will do a compression test and leakdown in the spring to see what everything looks like.