use a commercial grade of motor oil and forget ALL oil additives. over the road trucks run almost 24 hours per day pulling loads that are more than double their own weight and travel more than a million miles using an A.P.I. commercial grade 15/w40 or 10/w30 without lubricant failure,and with out oil additives .the crankshaft in these engines are three times heavier than automobile cranks, the rods are three times heavier, the pistons, etc. the water temp is greater the oil temp is greater and a host of other extremes that auto/ light trucks never see;and they do it with out additional additives.