I have a 2012 f150 stx 4x4 with the 5.0l flexfuel in it

My question is can I just go and put e85 fuel in it or so I need to buy something for my truck to use e85?

 

If it's got a FlexFuel badge, it's already set up to use E85. Nothing else you have to do.

 

Your manual will explain this in more detail. If you don't have one, they are available electronically. The key is to put at least 1/2 a tank in, and never less than 5 gallons, and then immediately drive at least 5 miles.

Note that the significant decrease in MPG requires that you save around 30% per gallon in cost just to breakeven. So take the price of regular (87) and multiply by 0.7. If the E85 is below that price, then you may save a bit. If it's above that price, you won't. In general you won't see that kind of price difference unless you're in a big corn-producing area.

From the 2012 manual:

It is best not to alternate repeatedly between gasoline and E85. If you do switch fuels, it is recommended that you add as much fuel as possible—at least half a tank. Do not add less than five gallons (18.9L) when refueling. You should drive the vehicle immediately after refueling for at least 5 miles (8 km) to allow the vehicle to adapt to the change in ethanol concentration. If you exclusively use E85 fuel, it is recommended to fill the fuel tank with regular unleaded gasoline at each scheduled oil change.

 

I tried using this fuel but the mpg loss did not make up for the cost difference. So I stopped using it.