Fuel question
 

I was just bought a 2003 f150 from my dad. We've had it for over 10 years and they've always run e85 fuel in it. i know the recommended fuel is 87 and want to start running it but before i did wanted to see if i needed to do anything to it before hand or fill it up with 87 and be on my way. any help is appreciated

what i would do is either run the truck till it runs out of the e85 or drain it out of the tank. it is not good to mix the two fuels

how many miles on the truck?

E85 is 51-83% ethanol vs the what, 10% or 15% in regular gas? So what is the issue in switching? It seems to me that the E85 is more corrosive on the rubber and plastics, but might gives a higher octane number rating. So regular gas would be less corrosive on the fuel system but might be more prone to the light pinging a lot of us get.

Wouldn't the real concern be in going from regular gas to E85? And since most pump gas already has 10-15% ethanol why wouldn't it blend ok with E85?

the truck isn't a flex fuel and shouldn't have ran on e85 to begin with

To my knowledge Ford did not start producing the flex fuel capable F-150 models until late 2005. There are however aftermarket flex fuel systems that can be added to some models that didn't come from the factory FFV capable to add that capability. On vehicles that are truly flex fuel capable, they are usually able to adjust on the fly as needed for changes in ethanol content. So most all truly flex fuel setups can adjust on the fly as needed when you are switching over from one type of fuel to another. However some vehicles that have aftermarket calibrations for E85 are setup specific for only E85 in which case you would want to try to run all of the fuel out first before switching back / fourth to the other type of fuel. Do you know if the truck has an aftermarket flex fuel system that was added to the truck before you owned it possibly? I would definitely double check to see the specifics before changing to a different type of fuel just to be on the safe side.

Hopefully the e85 has not damaged the fuel system. ethanol is corrosive to rubber and certain metals.
As said, it was not designed for it, but if you have been using it for 10 years and no problems, maybe you got lucky.
Surprised you have not been having drivability issues, these trucks are not mapped to run on the e-85 so it would be running lean and get horrible fuel mileage.