Thought just crossed my mind....ya'know what's really cool ? We never have a thread asking what the best coolant is to use.

^^^ SB , on my raw water cooled 502's , I usually use whatever coolant is available ( some may advise to check specific gravity , iron ,calcium , tannin content to see if it's even safe to enter fresh water lake ) salt water doesnt matter , it's only going to last a few months before it completely rots away.

Seriously , VR1 20-50 , is fine. I put about 40 to 50 hours a week on my 502 Mag ( parasail boat ). 100 hr service every two weeks ( oil change , drive oil ,ect.) . At 1500hrs ,I sell them with full buyer inspection . Most mechs cant believe they look so good . Drives are a different story , Never turn over 3500 rpm , blow the tops off Bravo 2's at least 3 times a season , even with 1000 gpm dedicated drive showers and MercSynthetic lube ( required for insurance liability).

Wow! I can't say that I've heard of anyone having engines last that long that I've read about yet but I'm new here. Are they MPI motors? Sounds like you go easy on them though so maybe that's the difference?

Sometimes 3500rpm is all you get when loaded and flying a big parachute . When I bought company , one boat had a 3 year old 496 with 3000+ hrs. Log books showed 30 something oil changes , couple sets of plugs , belts , idler pulleys , raw water pumps , but nothing major . Most engines dont wear out , they usually suffer a failure from lack of use , maint , or misuse , BTW I only use 496 style exhaust with dry joint stainless elbows ( IMO bad exhaust causes at least 75% of engine failures in salt water ).

My father in law is a officer in the coast guard and we were talking engine hours and he laughs at what we think is high hours. they put 5000 hours on black merc engines.
As for oil I use Joe Gibbs MR50 15-50 per egine builder recomendation

Are you talking about Merc black outboards or inboards? If inboards I need to find out what oil THEY are using! Lol.

I used to run VR-1 20w-50 but now run Amsoil 20W-50 Dominator as I am using Amsoil in all my vehicles ( motorcycles, truck , Porsche).

I'm not an oil expert but I have used 25hrs as a change point for years.

I have read where Racing oils are a one shot deal, fill it, race it, then dump it. I doubt any of us would change oil, go for a ride, dock up and change it.

Anyhow, 25 hrs on the oil, 50 hrs on the filter.