Originally Posted by Jeff Barnett (Post 1263)

I beg to differ on this. First off I have no connection with Mobil Oil, however Mobil One Synthetic, is the best oil an engine can have. I've done independent studies, with long term use, granted, these test were not marine application, but street, race track and long distance highway driving, at constant speeds. First off, once you go synthetic, you cannot go back. You should also never use synthetic until the engine is well broken in. In a car it's recommended at 6,000 miles. If you try and break an engine in on synthetic, the rings will not seal, yes it's that slippery. It's also not for use in pre 80's engines, as in small and BB Chevy’s from the 60's and 70's, they will develop oil leaks within 200 miles of use, crazy huh?Dino oil is just that, old dead Dinosaurs, that decomposed into crude oil, they leave deposits, and gunk on the internals after about 30,000 miles. Synthetic, has none of this, and maintains its viscosity far better than Dino oil. As for using 15w 50, that’s a bit heavy, does your engine pull good revs? It’s also a nice load on the crankshaft. 15w 30 is whats used in Corvette racing engines, they run Hi revs for a long long time. However if you are in a very, very warm region, and it works for you, it won't hurt other than higher oil psi, and slower revving.
I swear by it, having been using it for over 15 years, in all vehicles, and in car applications, I change it every 6,000 miles.