Ethanol separates from gasoline in about a month. If the gas sat at the gas station for a few weeks before you bought it, it can separate before you use it up.
Ethanol will eventually damage the rubber and other components of your non-ethanol-safe fuel system. These components can be replaced with ethanol safe ones.
Small engines in lawn mowers, snow blowers, chainsaws, etc. seem to be more susceptible to damage from gasoline with ethanol in it.
In some places, the high octane gasoline does not have ethanol in it but some cars do not run as well on high octane gas because the gasoline does not ignite at the most efficient time for the engine. Where I live, high octane gasoline has no ethanol, and mid grade gasoline has half as much ethanol as regular grade does. Apparently our mid-grade is a 50/50 mix of regular and high-grade. I don't know if that makes sense, but that is what I've been told by 4-5 different people.
My car does not get as good mileage out of E10 gasoline. I experimented with using high octane gasoline and found that, even though high octane costs more, the extra miles per gallon I got was worth the extra cost. This will likely not be the case in cars that do not run well on high octane gasoline.
In my area, we do have a few gas stations that sell ethanol-free gasoline.
> In some places, the high octane gasoline does not have ethanol in it but some cars do not run as well on high octane gas because the gasoline does not ignite at the most efficient time for the engine.
I don't believe this is the case. Gasoline engines with higher compression need the higher octane fuel because it won't ignite at the temperature and pressure in the cylinder prior to the spark plug firing. Once the plug fires, the temperature and pressure are right for gasoline of any octane level within reason to combust.
There's no downside to running high-octane racing gasoline through a low-compression engine like the Atkinson-cycle engine in the Prius, but no benefit either. Other engines, like the 5.0 V8 in the Mustang GT, have different performance ratings for different grades of fuel. Still other engines, like the 2.0T I4 in the Volkswagen GTI, require high octane fuels for the extra compression they run.
If the engine has adaptive ignition (retards spark in response to
pinging/detonation) then using lower octane fuel in a
higher-compression engine may not result in engine damage - just
less power.
OTOH, using higher octane than the manual / engine specs call for is
just a waste of money for no extra power - but is not damaging to
the engine.
One of the less-noticed issues with ethanol as a fuel is that it
contains/provides ~33% less energy than gasoline[1] - so saving n%
per gallon at the pump may cost you n% in mileage down the road.
[1] http://www.eia.gov/tools/faqs/faq.cfm?id=27&t=4
More stops for gas might benefit fuel vendors by providing them more
opportunities to sell you higher-profit impulse or convenience
purchases over the counter.
> Apparently our mid-grade is a 50/50 mix of regular and high-grade. I don't know if that makes sense, but that is what I've been told by 4-5 different people.
Yes, typically gas stations only have two tanks of gasoline: low-grade and high-grade. When you select mid-grade it's blended at the pump.
What do you drive? Typically the only cars that get really poor fuel economy with "Regular" are cars that specifically call for "Premium". When you fill them with "Regular", the computer essentially puts the engine in emergency limp-home-mode to prevent catastrophic damage, which reduces power and efficiency.
I drive a 1996 Honda Accord EX. It gets better mileage on Regular than Premium, but better mileage on Premium than E10 Regular, even after factoring in the price difference.
