I’m just doing an informal survey of how many people out there have or know of well maintained high hour 502 mpi mags still running good??
I have about 720 hours on mine and they still have the same performance and oil usage they did when I got the boat at 220 hours. No issues other than normal maintenance. Any out there with a 1000 +?

Thanks. John

I have 527 hours on mine, runs great makes the same speed as when new. I haven't had any problems except those dam plastic pulleys Merc used in 98. The power steering one went last year and this year the pulley on the sea water pump went.

I have always used synthetic oil. Mobil 1 at first but a few years back, I switched to Royal Purple 40 weight.

About 525 hrs on mine with nothing but regular maintenance. They run the same as they did 300hrs ago.

+1 Mine has "way over 500" and runs like new. I'm anal about maintenance and have only run Merc 25/40 her whole life. I did have the top end done around 500. She'll burn a quart every 25 hours if running "hard" ie + 4000 RPM.

Hope none of us are jinks(ing) ourselves.

Im in the 6-700 hr range. Just had to do a top end this passed off season due to clogged fuel injectors, witch blew my headgaskets. Other wise strong engine. 135 spi each hole, and about a qt of oil every 3 tanks of fuel or so. Im very impressed with the 502 mag efi and it reliability.

i have the same engine essentiall (454 mag) in my baja, that my buddy now drives. with the headaches im having with my new boat, i wish i still had it...anyways close to 700 hours and fires every damn time! kinda frustrating, lol, but only regular maint/impellers/water pumps have been changed.

Buddy of mine has a 502 mag with 800+ hours in his scarab. All stock.

F.Y.I., the 720ish hours on my 502 Mag mpi’s were all with 25w-40 Merc oil for the first 375 hours and the rest with Merc. 25W-40 syn. blend.
I never run the boat hard till the engines are fully warmed up, and mainly stay in the 2800-3200 rpm range, but there are plenty wot runs in there too.
I have been using the Merc hi efficiency oil filters or amsoil oil filters with filter mags on them.

Are you guys gettin these hours out of the 502's with the original valve springs?

Is the often read "you have to do valve springs at 200 hours" language bogus?

Also, I've read stuff about a low tension piston ring set bein used at some point that need replaced relatively early too. What years would this have occurred or is that bogus info too?

that would be a 502 block(blue) 500hp carb engine,,,they are talking about the 502 efi (black)engine..