Hi Tim,
There are two potential problems, both caused by ethanol in the fuel and both
exacerbated
by long periods of inactivity.
If you are experiencing a blotchy opaque jelly like substance that sinks to the
bottom of the tank and collects in your filters, this is most likely water
contamination
in the fuel that has undergone phase separation - the ethanol combining
with more water than it can bond to, eventually drops out of suspension.
Typical causes are a leaking fuel filler cap letting water in during heavy rain,
or condensation forming in the air space of a half empty tank in an aircraft
that has been left standing for a long period of time during the misty, clammy
or humid winter months.
The second problem really is a bacterial infection. Airborne acetobacter that
breed
during the autumnal months in the fruits and berries found in the countryside
can come into contact with the ethanol fuel via the tank breather pipe. These
feed on the alcohol and produce acetic acid as a by-product. This turns the
normally non-conducting fuel into a conducting mild electrolyte. The acetic
acid will then begin an electrolytic reaction between the brass and copper
components
in your fuel system and the softer alloy components - which will corrode
ferociously. The most obvious place to check for this is the Bing float bowl.
Our aircraft have the same life cycle as our lawnmowers. They get dragged out in
the springtime, are used on weekends (if the weather is good) and then get
dragged
back into the shed/hangar in the autumn and forgotten for another five
months. Problems almost always occur after the planes are left with half full
tanks (big air space) for long electrolytic of time.
Cars, that use the same fuel don't seem to experience the same problems because
they are used throughout the year and fresh fuel is constantly flushing through
their fuel systems.
Since we can no longer get mogas without ethanol, the only way to prevent this
contamination/corrosion is to ensure that the tanks are always left full at the
end of every flight (the least possible air-space in the tank) during the flying
season. At the end of the flying season, the tanks should be flushed, or
run dry, then filled with a few litres of 100LL (that does not contain ethanol)
and the engine run to draw this through the whole system. The aircraft can then
be laid up.
I have pictures that illustrate of both problems - but can't post them up at the
moment as I am away from home.
Hope this helps
Nigel
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