They wouldn't use Amsoil because there isn't anywhere on the oil package or website that states that it is to be used on marine outdrives. If anyone has any data on this, please share. I ended up signing a waiver, and got them to use the Amsoil. Considering that Amsoil has always been run through the drive for the entire 200 hours, I would like to continue that. I hope that I made the right choice, as my mechanic acted like I was crazy.

If you go to www.amsoil.com look under gear lube I believe. They have a product that is labeled Marine Lube or Marine Gear Lube. To me that says it all as far as specific use. As for the Severe Gear Lube... I've never seen any literature that states it's for marine applications so I didn't go that route although many people on this site say they use it. What product do you run?

The guy that I bought the boat from swears up and down that the Severe Gear is the best, and that is what he has run in the drives. I ordered the Severe Gear, but the fact that it doesn't say anything about a marine application has me worried. I am not a racer, nor do I run the boat very hard. One part of me just wants to have them go ahead and just use the Merc HP lube. I want to use a gear lube that is going to lead to the long life and dependability of the drive. At this point, I'm not sure what I'm gonna do?

I'm sure that either way will be just fine. Chances are if you get any water in your drive, it will be a total failure by the time its discovered anyway. I wouldn't loose any sleep over it either way.

I agree. When we're talking about such high quality products as these, we're probably just splitting hairs.

I went ahead and had my mechanic use the Amsoil Severe Gear 75W-90. The boat ran great last year with the same stuff, and "if it ain't broke, don't fix it." Thanks for all of the information guys!