I like the Mobil 15W50 also due to the high
zinc and phosphorous, the problem lies in the fact with a 9 quart system it takes forever to get the
oil warm enough for it to flow. When using 10W30 it pumps out of the rocker arm and fills the void with little overlfow. The majority of flow goes through the needle bearings in the rocker arm fulcrum instead of splashing over exactly where you want it. The 15W40 just overflowed the rocker arm with little going through the bearings. It was similiar to pouring water through a screen and pouring syrup. If you are trying to wet what is below the screen you want the water.
With 10W30 my
oil pressure is 35 psig at 90C and 40 psig at 80C at 900 rpm. Anything above 1500 rpms it is 53? psig. At 100C and idle it is 30 psig.
With 15W40 add 8-10 psig everywhere.