I'll keep an eye out for that AC 15w40. Of course I could always get Valvoline Premium Blue. Also plan to go to Motor City Truck-Ford/Sterling sometime to check out their oils and get some FleetGuard filters.
I don't see where there is a problem running 10w40 in the pickup ('95 F150 4.9L), even though the owner's manual says 10w30 and allows 5w30 when below zero. My Haynes manual for this truck ('80-'96 has a chart that allows everything from straight 30 to 20w50 (in appropriate temperature ranges). Tollerances (variation on a surface) may be tighter, but clearances (distance between moving parts) are relatively unchanged. A 10w30 will act line a 40 weight somewhere below 100C and manages to get through the galleries OK. I guess the 36 psi is plenty, but I get a warm fuzzy feeling having it above 40, even though the 40 does stretch the oil a bit farther with VI improvers. As for good oil pressure for a Ford, my '90 460 V8 runs 70 psi cold, 58 hot at 2000 rpm, and 27 at idle hot.
A 15w40 should be about the same at 100C as a 10w40, but will stand up to abuse better since it has less VI improvers and has a heavier base oil (as is apparent in the higher HTHS number on a 15w- vs a 10w- oil). So I think I'd really like to try this 15w40 stuff in the summer. When I drive it long and hard the pressure will drop a few pounds (sure wish I had a temp gauge to see what might be going on) and with a 15w- it may not do that--will see. I am a Maxlife user and may try mixing equal parts 10w40 and 20w50 to get a sort of 15w40 (albeit, pushing the upper end of the 40 grade range) and it would be a dumbell oil (no not to insult myself, but talking about a dumbell frequency curve to the oil molecule distrubution with two humps, one in the 10w range and the other in the 15w range). Anyway, it should be an interesting summer.
[ December 07, 2003, 12:38 AM: Message edited by: TallPaul ]