Hi, I am new here. I have been boating my whole life but just made my first boat purchase. It is my understanding (based on the manuals I have found) that these engines can run fine on 87 octane. Does 89 or 93 help at all? Do I gain anything? I put some in but am I wasting money?

Engine is a 97 502EFI Mag with 265hrs.

Thanks

P.S. I did search, but came up empty.

Nope,
87 is perfect for the engine, and Welcome to OSO!

Yup, 87 is fine. Just don't let it sit around too long.

Cool! Thanks guys! Saves me like 10% in fuel costs!

So far this site has been very informative! Great site! And very responsive!

If you can purchase 87 without ethanol, do so. Welcome!

everyone else here is correct but for the 10 % more i would run the best fuel i could buy whereever you are . its safe insurance. if you get bad low octane fuel which can happen at most marinas with in ground tanks, then you have bad fuel. if you buy bad higer octane fuel, that might be good enough to save you.
everybody that says 87 is correct... on paper. i'm simply talking about what happens in the field . certainly if you are trailering and filling up at hi volme name brand land based stations then you are in good shape no matter what you buy.

I only fill up on the trailer on shore. It's about $1.50/gal more on the water here.

Well I hope the 50gal of 93 I put through it already, helped clean up the fuel system if anything.

What about fuel treatments? Anything special I should put in and how often?

Sta-Bil, along with helping to keep your fuel fresh, also acts as a carb/fuel injector cleaner.

the trick is , as discussed elsewhere, not to let your fuel get old. you buy what you can use in 30 days and for the winter you put in a little dry gas, and marvel mystery oil, start it and run it for a bit the shut it off and drain it dry or as dry as possible. i don't reccommend stabil or any of these other snake oil additives. theyre ok for your lawn mower maybe... but thats where it ends.

Those are great reliable engines stock, I have about 620hrs on mine untouched and they run as good now as when I got them with 200 hrs. I have only used the pure gas non ethanol fuel in mine, which is suppose to be a 89-90 octane.