I just bought a 09 ranger z520 with a 250 pro xs merc...my last boat had a yamaha 225 hpdi and i have 4 cases of yamalube left over.. I have had 2 guys tell me that all the oil is pretty much the same thing and i will be fine running yamalube in my merc...They tell me that merc just wants you to buy their oil and yamaha the same thing...Can anyone out there please enlighten me on the true facts???????

Considering what that outboard costs, buy the Merc oil. Follow the manufacturers guidelines, its always the only safe bet. That way if something happens, you don't have to worry about it. Technically they may not be able to cancel your warranty for using different oil, but isn't it worth it not to have your boat down for a powerhead replacement and all that jazz? To me, its worth it.

I would get the Premium Plus so you don't have to worry about it. Every Merc mechanic I've ever talked to has said emphatically to use the oil the manufacturer recommends.