Originally Posted by Skill_Kills
a buddy of mine was out of town and it was going to drop between 40-50 below and he didnt have anywhere to plug it in so he filled it up parked it for 9 hrs and only had to put in about 3 gals. so yeah about 1/3 gallon/hr. im sure it has quite a variance from truck to truck but he told me its in the manual somewhere as about a quart/hr (i have not read this so i cant verify whats printed)
regardless of what it actually is, its nothing to be worried about for 20-30 mins if it means your engine is nice and warm before using it.
I pretty much have all the manuals and I can't find it in them (I could have missed it, but I do spend quite a bit of time in the manuals). Also, if your friend hasn't installed the harpoon mod, then there is no way to be very accurate in his test.
Also, Ford says don't idle for more than 10 minutes unless you have the high idle. I know folks that do, but you will generate more soot idling at 750 rpm's and it can eventually bite you.
Additionally it takes around 10 minutes of high idle
to get your coolant up around 150 degrees F - when the weather is in the mid 20's. Regular idle is not very effective in cold weather at warming things up very fast.