I have been using Amsoil 15w-40 Heavy Duty Diesel and Marine oil in my boat. I change it only once per year and put around 100 hours on it. The engines are 8.1 liter GM that are marinized by Crusader. The engines run at 1,500 rpms half the time and the other half at 3,500 rpms. This boat is heavy at 26,000 lbs. so it is quite a load. Is there a better grade of Amsoil that I should be using? When the oil says Heavy Duty and Marine I am just assuming it means any marine engine, diesel or gas like mine. Any thoughts by you Amsoil gurus?
100 hours is comparable to 5000 miles on a road vehicle. In that case, you are more than fine. Mostly the 15W40 is an oil for Diesel Vehicles. You may find slightly better performance from an oil designed for gasoline use like a 5W30 or 0W30.
Hey Silverton Cummins has marinized the 5.9. It makes as much hp/tq as the 8.3(480/900) and is much lighter. Just an FYI for when you're ready to change over...
