We all know what a pain getting fuel can be on floats and now and then you have to put in auto fuel. This information is posted on the STC website. I made a little tester from an old test tube and rubber stopper I had kicking around and it works just like they say. Auto fuel has also really gotten bad, products like STABIL help but shelf life is a couple of weeks at best. Worse there are reports of ethanol showing up in fuel sold as ethanol free. Your STC is void if there is ethanol in the auto fuel.
Testing fuel for ethanol
The following test can be performed to determine the presence of ethanol in gasoline.
On a test tube or olive bottle, make a permanent line about two inches from the bottom.
Fill with water to this line, then fill the tube to the top with gasoline.
Cover the tube, agitate it then let it stand.
Ethanol mixes with water and the two will separate out together. Therefore, after mixing the water and the gasoline, if the water level appears to have increased, then the fuel contains ethanol and should not be used.
Ethanol fuels can damage the rubber and aluminum components of your aircraft fuel system. Ethanol increases the volatility of fuel, and hence the possibility of vapor lock also increases. Ethanol may vent off at altitude, reducing both range and octane. For these reasons fuel containing ethanol must never be used in airplanes.