IRONMAN

Valvoline VR1 20w50. But to correctly answer your question oil viscosity will vary somewhat based on air and water temps you run the boat in.

BUP

iTrader: (9)

^^^^ will agree and will add oil viscosity - a big deciding factor is what your bearing clearances are set up at.

A good example of this is the Indmar and the PCM marine GM LSX (550 /556) requires 5 w 30. motor oil and some other of their GM based marine engines require 15w - 40

apollard

+1

SB

iTrader: (1)

IMHO - don't let someone talk you out of something that has worked for you for many years. Factory 502's aren't the most 'tightest' engines.

cgpsu309

x2

Fordtrucks

Amsoil Dominator Synthetic 15-50

Keith Atlanta

+1 With one quart of Dominator 60 weight mixed in.

Smitty

iTrader: (1)

Gibbs Driven synthetic 15-50. Keeps great oil pressures even after hard runs.

BUP

iTrader: (9)

^^^^ yep I would stick with that to.

MILD THUNDER

iTrader: (3)

Did these oil experts ask you what your bearing clearances were, or what oil temps you see?

I'd have a hard time switching from what's known to work after 10 years. Some of these "oil experts" can't get an engine to live for 10 minutes.