I have recently converted my 99 Corvette to run Flex fuel. How long could I keep the E85 in the tank before water separation occurs? This is a weekend driver. Should I use any ethanol treatment in my tank, and how often should I use it?

 

Just out of curiosity I did a quick search, and found this information readily available....and obviously not unique to a C5.

Just one example: https://eflexfuel.com/us/blog/does-e...FFUa9BrNQyPpDg

I'm sure CrapGPT has a wealth of info too.

 

You're fine for a weekend driver. Off season if you park it you'll want to actually drain it or consume it all and get it out of your fuel lines. It eats the seals on the injectors and rails and can eat any rubber line you've used. PTFE or metal is preferred. The tanks are OK. The oem pump may not be.

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Unless you've replaced all the "rubber" components dealing with the E85 gas, you'll get problems eventually. Question: why would you run E85 (more expensive as I recall) in a Vette? Save the environment? Buy a Prius as a weekend car!

 

you forgot the part that it is cheaper and it gave me 80 rwhp more

 

Cheaper, I don't know. Maybe? None sold around here. 80 more RWH? From 5% more corn oil? Very hard to imagine. Pure alcohol based race gas, sure. All I remember from my stint in the midwest, very long ago, was it cost more and my gas mileage was much worse.

 

Modern flex-fuel emissions systems are set to pull the fuel tank into a vacuum while the vehicle is off , the fuel tank vacuum is monitored for sealing.
Sealing away the tank is necessary to keep atmospheric water exchange out of the fuel tank, which preserves the quality of the alcohol which would otherwise continually absorb water from the air.

As water is pulled into the fuel tank from air by the alcohol the alcohol becomes more corrosive to metals inside the fuel system, the water allows corrosion and oxidation to occur at the metal-alcohol interface as electrons use water molecules to 'get around' an energy barrier.
Although a phase separation is possible it isn't necessary for the absorbed water to start attacking and damaging the fuel system components.

When retro-fitting a non-efi or non-flex compatible vehicle with flex fuel alcohol it is necessary to check valve the fuel system inlets/outlets and monitor the fuel tank pressure, maintaining its seal and preventing water from gaining entry while the vehicle sits.

 

Being ignorant of fuel systems as far as the function of the emissions system on the intake, what can you offer on this. On my 2003 I heavily modified the tanks by adding bulkheads and running my own lines across externally with added length of hose to allow far easier service if ever needed on the driver tank which has a primary and hobbs switch secondary pair of Walbro/Ti 450 pumps. The infamous crossover tube is now a mere 5 second disconnect / reconnect and my fuel feed lines are separate from any former OEM lines, now running forward to an AFPR/return and a line which terminates on the rails like the C7 Z06 would. The (evap?) line from the tanks up to the (purge?) solenoid up front I simply cut mid torque tube and left open. The car isn't running yet but will be soon. What am I looking at for pros/cons if left as is?

 

When I switch from 93 Shell to Speedway E85 I see a 75 WHP increase? E85 is over 100 octane, on the order of 105. Plus it cools the charge air by 150 degrees.

Where do you get "5% more corn oil"? E85 is up to 85% alcohol.

Gas mileage? You are in the wrong conversation. LOL

 

(S)miles per gallon

 

The fuel tank and crankcase is like a bottle of soda or vodka, with many exits and entrances and some flow both directions. Many vehicles have a gas cap with a check valve that allows air to enter the tank but not vent out for example. When a tank has a simple vent, the fuel/soda goes flat and loses important constituents(fuel 'goes bad' if left out to vent) and alcohol gains water which attacks the fuel system over time. Novice enthusiasts get around this issue by constantly changing the fuel in the fuel tank before it degrades much. Modern proper fuel systems prepare multiple entry/exits with failsafes to prevent over/under pressure. Just like an engine crankcase pressure, the fuel tank pressure and fuel temp are control variables people seem to rarely consider. To keep fuel as high quality and the engine as clean as possible is part of filtering and sealing the fuel away from environment and controlling its products after the engine has burnt some percent of it. Putting in high quality fresh fuel, burning it completely with clean engine parts at a favorable (low carbon) product condition(lean and modern chambers) is all part of the same big picture of high mileage without carbon buildup and original piston rings in great shape.

 

So.... This little plastic tube 4 feet from the tank... Cap it, or reconnect out to somewhere/something. I honestly never paid attention to this function or line as it is emissions related or so I thought.

 

A lot of bad info here:
First, E85 is the cheapest option at the fuel pump. Right now in Northern CA E85 is $3.19/gallon, 87 Octane is $5.49/gallon

The rubber fuel components only applies to very old vehicles that have never had their fuel components replaced. Every fuel line and gasket made after ~2000 is E85 compatible.

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During the 10 years I daily drove my Flex-Fuel Subaru, my general rule of thumb was to run a tank of 91 Octane through the car every 6 months or so. If there was water build up, that would flush it out. When it was really cold out, I'd run on 91 Octane just to make the car warm up more quickly.