yeah that will be fine

 

I'd run it empty... just fill up a 5gal tank of 87 and keep it with you, when you run dry of the e85 pour in the 87 and then head to a gas station.

If you're nervous about running out of gas, wait till the low fuel light comes on, then drive a few miles (I know I can get at least 40miles when mine comes on) then when you're really low just do laps around the neighborhood till you run out. That way you can run out in a safe area and fill up.

 

Why run it empty? That will just be a bigger shock. Start using plain old 87 octane E10 now and as the blend changes more toward E10, less ethanol, it will either start running worse and you know you have a problem or it will run fine.

 

There's no "shock," because the EEC was never designed for different fuel types to begin with. It doesn't know the difference between E85, E10 87, E10 93, or anything in between. It uses the preset tables it's programmed with.

2100 has it right, except the in-tank fuel pumps in these things don't like being run totally dry (or for long periods with minimal fuel), since it's the fuel that cools them. I'd run it until the light comes on, drive it another 20 miles, fill it with 87 octane, and enjoy it another ten years or so.

 

Yeah I was hesitant to change my wording because yeah technically really nothing should be ran completely dry lol. I was figuring when it started stuttering he'd shut it down and fill it up. But I also know people run out of gas all the time and it doesn't necessarily mean you're gunna destroy the truck. So yes OP you don't need to run it till its bone dry but get as much out as you can.

Edit* also not a bad time to find out what your low fuel light means. Like I said I know I have at least 40 miles once my light kicks on. (Stuck on a barren stretch of interstate and was hoping a gas station was coming up.... it did 42miles later) I've got 35s and cant recall my gear lol so your light estimation will probably differ. But it's always good to know how dire your gas needs are when the light shows up. I've not dared push it farther because I'm rarely 40+ miles from a gas station.

 

True. It's just a safer bet to leave a little in there.

 

That's why I added the last sentence I agree lol

 

The PCM settings will probably change with E10 versus E85. Call it a shock, call it a change, whatever. You might get some funky idle behavior or a code.

But, it really doesn't matter much. There's no reason to drain the E85 down before filling up with E10. What is the rationale? There isn't any.

 

Even the user manuals for flex fuel vehicles say to run the tank low and fill it up with as much 87 as you can. Granted they say half a tank is do able; even FORD recommends using as much as you can before switching and not to switch often.

Also these trucks weren't supposed to be running on E85 so best to run it low and fill up with 87 and not mix the two.

Why does FORD recommend you run it lower than at least half but preferably lower? There isn't any reason to argue with FORD unless you just like to argue.

Edit* link if you want to read. Last paragraph is what I am paraphrasing from FORD
http://www.fordservicecontent.com/Fo...ngEnabled=True

 

The PCM will *not* change anything, since it has no way to know that a different fuel is/was being used in the first place.

As to the second part of your post, mixing the existing fuel with E10 will simply prolong the existence of higher levels of alcohol than should have been there in the first place.

OP, if you really wanted to, you could remove the Schrader valve from the fuel rail, run a hose to a bucket, then run the truck using the fuel pump to drain the tank. That would actually be the *quickest* way to eliminate the E85. After ten years, though it probably won't make much difference any way you slice it.