This was the inside of my tank after sitting for a few years with the lines open. Pump was ruined as well, I had plans of replacing it all anyway.

 

Yeah... I mean... kinda expect that.

 

Not sure what any of these "I had the car sit with an open fuel system for multiple years and look, it's ruined" posts are all about.

Next we will see someone posting an open block that sat outside for a year and is rusted.

 

Been using E85 on and off for the last 4 years now, often leaving E85 in the tank over multi-day periods of being parked. About half the time I drive I run gasoline through it. Currently at 180k on the engine and chassis, started E85 with a Haltech Elite and a flex sensor at about 140k.
I checked the pistons with a borescope a few thousand miles ago and I was amazed at how clean they looked even with the high mileage. A tiny bit of carbon build up but otherwise they where beautiful! I was really surprised because I've seen pictures before of the carbon buildup and was always concerned.

Then these last few months I haven't been driving my Evo very much so I parked it in the garage with a maintainer. Busy with a ton of work, I forgot I left it with a quarter tank of E85 plus what ever was left in the lines. After almost 6 months of sitting with E85 in it I realized my big mistake and decided to deal with it.
I removed the fuel pump assembly and inspected the tank. It looked the same as it did when I bought the car. No residue, no build-up, really no grime of any kind. I was very pleased. The E85 still smelled strongly of ethanol. So at this point I decided to drain the tank of as much of the E85 as I could while still leaving enough to drive to the gas station. When I removed the fuel lines to drain it they ll looked completely clean as well. No gum, no residue. I drove to the gas station and stayed off any real power, although the car had no trouble taking light load. Refueled with a full tank of 91, drove it around for a bit and everything was fine. No weird AFR spikes, car ran clean with no misfires and was quick and responsive. Overall it seems like leaving the E85 in the tank/lines for 6 months had no effect. I again inspected the pistons after driving and they looked like they had a tiny bit more carbon than before but no real major difference. Still looked clean. Spark plugs showed little fouling.

Take my entirely anecdotal story as you will, but in my experience E85 has no detriment on the fuel system long-term, although I wouldn't recommend leaving E85 in the tank for extremely long periods of time. Only thing I've had trouble with in the past is the fuel return line in the engine bay, for whatever reason I've had to replace that hose with something ethanol compliant on almost every Evo I worked on as it would leak fuel. If anyone's interested I can post pics of everything when I checked the lines and piston tops.

Also obviously, don't leave your fuel system open to the elements. Leaving any part of the engine open to elements in general for extended periods of time is generally a big no-no. I was really hoping common sense would prevail on that one...

 

For what it’s worth, my tank was damaged from the car sitting on the ground without suspension (previous owner). My post was more of a “this is why you shouldn’t leave your fuel system open” than a complaint. It was that way when I got it