Conventional or Synthetic oil?

[Bad Habit]

 I have a 1987 5.7, 260 hp Mercruiser engine with 4600 hours. I have been running 30 wt oil in it since it was new. I was wondering if there would be any benefit to running synthetic oil in it. I was told awhile back that there isn't but not sure what the reason was. 

[fisherdude]

a 29 year old motor with 4600 hrs on it, i would think the oil you are running did the job just fine . must have a good maintenance schedule as is 

[thumbburn]

Keep it the same

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[tinfin]

Don't fix it if it's not broke, seems like your maint. schedule is excellent!

[lakebound88]

Synthetic only benefits a motor from the get go after break ins..

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[jimski2]

Synthetic oils are needed for high operating temperatures above 180 degrees to comply with gasoline mileage issues of your newer cars. Mineral oils oxidize the oil and cause it to fail quickly when temperatures above 180 F is operated. Most boats operate at 160 degrees as it is a safety issue.

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[Captain Carl Bish]

I bought a 5000+ hr engine that I changed over to Valvoline Max Life when I bought it, I got at least another 5000 out of it before it gave up the ghost.   For what that is worth. 

[slow rollin]

Keep running the same oil all synthetic will do for you now is make you lose weight. From your wallet! That's a ton of hrs on a motor synthetic won't take the hrs away.