Originally Posted by fordpwrstroke7
I don't have my owner manual in front of me but I think -40 is BARELY past the point where Ford recommends plugging in the block heater. While -40 is cold, it's not necessary if you're wanting to avoid cold starts if you have a block heater.
-40 is cold as Chit. Anyone who has ever tried to start a truck in -40 knows that it MUST be plugged in to start, and even if you let the truck idle, you will still be loosing engine temp faster than your gaining temp if you dont have a cold weather blanket on the grill(dont ask me how I know this
) . My truck has idled in temps that cold, but I have never started it that cold. THe coldest I have ever started my truck in with out being plugged in was -15, and it started but was pissed off for a bit. The 6.4 starts alot easier than the older diesels did, but at -40 you are still going to have issues. I would say go ahead and let that thing idle. You will be fine. I have let mine idle for 6+ hrs before with no issues.