Originally Posted By: Panzerman
5w20, 5w30 ,10w30 or 10w40. Anything would be fine in that 4.6. We have company trucks with over 200,000 Ford F-150's with 4.6 engines, a steady diet of 10w30 and abusive company employees.
That reinforces my understanding that most engines out there are really not that sensitive to the difference in visc between a 20, 30, or 40, and you've got a thinner but still substantial oil film thickness in the crank journal bearings with a 20, something around a 5 times Stribeck Curve margin.