How do you convert your engine to use E85 ethanol mixture?

You don’t need to, the car is already E85 according to this site

Look down to Ford 1999 to 2004 3.0 liter.

Flex fuel means it can take E85. Just put it in and go.

What about the unleaded in the tank now?

and what if E85 Ethanol is unavailabe in other states I go to? Can I use both?

From @Tropical_Willie‘s link: “Flex-fuel vehicles (ffv’s) are designed to run on regular unleaded gasoline and an alcohol gasoline blended fuel, either ethanol or methanol, in any mixture.”

Will one gallon E85 take me as far as one gallon gasoline? Does it increase my cars value also?

FlexFuel’s can use both, at the same time. Last time I checked, it was recommended that you mix the two. When I first got my SUV, which is FlexFuel, I looked into the whole E85 thing. Unless stuff has changed in the last three years, one gallon of E85 will not take you as far as a gallon of gas.

And, of course, there’s the whole fun of even trying to find a gas station that has an E85 pump. In my area, the capitol of Texas, home of the New Californians, there’s one that I know of. Don’t expect to save a lot either; here, at the sole gas station, E85 was always 10 cents cheaper than regular. Always. And given that the fuel economy for E85 isn’t as good as gasoline, it all worked out to be the same in the end.

Ethanol has considerably less energy per gallon than gasoline, so expect your MPG to drop about 25% on E85.

Using @mrentropy‘s figure, you will probably save 2–3% per gallon (ten cents a gallon is a small savings when gas is around $4.00!) but using about 25% more gallons, so… unless yo make your own fuel, you really aren’t accomplishing anything :p

Ethanol is more corrosive than straight gasoline. Modern flex fuel vehicles are made to reduce the effects, but it is not a perfect system. Back when gas was about $2 a gallon my sister said it made sense to use the E85 because the savings made up for the lower fuel economy. Once gas passed $2.50 she stopped buying the E85 as it didn’t make economic sense.

It should go without saying that older cars (like the ones I have always had) don’t do well even with E10. In fact, Germany only uses 5% Ethanol and refused to go to E10 because many Germans have older cars like mine. Of course, the US government doesn’t care if they cause damage to our engines :/

Ethanol is a powerful solvent. It’s not really “corrosive” in the sense that it will cause things to corrode (that is, to deteriorate due to chemical changes like rust) but it can and will dissolve things that gasoline will not, like many forms of rubber (i.e., your fuel lines) and rust (like the stuff in the bottom of your tank).
The dissolved stuff then winds up in your carburetor or fuel injection system, blocking fuel channels and fouling jets or nozzles. This is a drag, but not terribly difficult to fix.
In most cases, ethanol use will not actually damage your engine. If you have a flex-fuel vehicle then you don’t have to worry about any of these things- the vehicle has been engineered to avoid problems of this type.

If an engine is older and worn (excessive piston ring clearance) and operated in a cold environment then it can happen that unburned ethanol and water (ethanol is highly hygroscopic, unlike gasoline) can end up in the crankcase, compromising the lubricity of the oil. This can cause excessive bearing wear.

I’ve not personally used ethanol in a vehicle (except for that in “oxygenated” fuel in Washington State which is typically ethanol not MTBF)- all this information comes from people I know locally who are biofuel users (the solvent problem also occurs with biodiesel, which is why older diesel engines need to have their fuel supply lines replaced with nitrile) and from the northwest-biofuels email list. Take it for what it’s worth.

In order to convert an engine to run on ethanol (e100) it ideally should be rebuilt completely. Ethanol has a significantly higher octane number than does any form of gasoline, so it should be used with a significantly higher compression ratio, similar to that of diesel engines. From what I’ve seen 14:1 to 16:1 are about right.
Usually this is not feasible to do. People who have converted conventional engines to run on straight ethanol (not E85) usually do the following:
1) replace fuel lines – ethanol will dissolve natural rubber and many forms of artificial ‘rubber’. Replacing the fuel lines with steel ones or lines of another non-alcohol-soluble material.
2) Incorporate a fuel heater. I’ve seen some conversions where the last few feet of fuel line wraps around the header before going into the carburetor. Ethanol is much less volatile than is gasoline, so heating it up is sometimes necessary to get it to vaporize, particularly in cold climates.
3) Completely clean out the fuel system before driving anywhere. In practice, most convertors I’ve met or heard about just add a few extra in-line filters to the system and let the ethanol clean out the system for them. Gasoline is a mixture of several different compounds, and over time some of these compounds decompose in the system and form varnish which sticks to the bottom of the tank and to other surfaces. Ethanol will dissolve this stuff and clog up a filter element (or your carburetor if filtration is insufficient) quickly. After you’ve gone through a few filter elements the system will have cleaned itself out and will stay clean after that.
4) Many convertors also replace the fuel pump, as some pumps allegedly work better with ethanol than with gasoline.

Conversion to E85 is probably similar but not identical. A quick google search reveals that there are many vendors selling E85 and flex-fuel conversion kits.