Well the oil pressure on the ol F150 has been slowly dropping. I recall when I first installed the mechanical gauge in 93 that I was getting around 40 psi at 2000 rpm hot. The other day I was driving her hard and the pressure was around 32 at 2000, so I stopped at an auto parts store and got some blue bottle STP engine treatment and dumped it in. Instantly boosted it to 40 psi. That stuff is about 200+ cst viscosity vs the oil being about 12.5 cst, so now I am running somewhere just under 16 cst. Should have used the Valvoline Synpower additive but not sure that is made any more. But from now on this truck will run 10w30 winter and 10w40 with a quart of 20w50 added to it for summer.