When ethanol first came on the scene, we started to test it in the lab. The fuels with ethanol cleaned out our fuel systems and caused a number of leaks. Most people think that when a fuel line is made of neoprene or Buna-N rubber that the name completely defines what that rubber is. What they do not know is that there are a number of different compounds of each of these products. When we ran hardness and swell tests on a number of different compounds of the more common rubber types, we found that ethanol affected them differently. For example, we found that some neoprene rubber hoses worked well with ethanol-containing fuels, but others would harden or swell a great deal. This means if a person drove a car or flew a plane with ethanol-containing fuel and did not have any problems, it only means that the rubber components in that particular vehicle were OK. It does not in any way, shape, or form prove that ethanol will work on all rubber fuel components. Likewise, there are a lot of different aluminum alloys — many that work with ethanol, but there are some ethanol will corrode.