What about my using E85 in my 1979 Chevrolet Monte Carlo?

-----I have a single-owner 1979 Chevrolet Monte Carlo, special-ordered in 1978, with the larger engine.

It has about 109,000 true miles on it.

I have replaced the alternator and A/C a number of times.

Outside of minor tune-ups, the engine has not been touched.

I have been using E85 in it, thinking it was totally interchangable with regular 100% gasoline.

My milage is way down with E85, to about 7 MPG in big city driving.

What can I expect if I continue to use E85?

I appreciate the time and effort it takes you to help me.

---Jim
P.S.(1): I mean, what can I expect overall, not just on milage. Can my engine be damaged?

just about anything rubber in the fuel lines to rot out, possibly causing leaks and a fire. also the timing is off on it, if you had it tuned up running on regular gas when it was tuned. e85 capable vehicles are set up with the computer to change the timing to compensate for e85. also your car is probably running to lean on e85. You could make your car capable of running on e85, by richening up the mixture on your carb, and advancing your timing slightly.it may also be wise to switch out your rubber fuel lines to newer fuel lines. You still wont ever get as good of fuel mileage with e85 as with regular gasoline just because it doesnt have as much energy potential as gasoline, but you can make it work.

Lower efficiency is one of the downsides of E85.

a blown engine stop using that stuff now the motor was not made to run on it.