I don't know anything about whether or not to use an alcohol free stabilizer if your gas contains ethanol. What I do know is that you should not completely top off your tank. Expansion will occur and you will have fuel leaking from the tanks expansion valve. I learned first hand about this early last spring when the boat above mine in our rack storage leaked on my boat and several boats below. I lucked out, but others suffered gel coat damage. My mechanic said to fill the tank between seventy five percent and full, and add an appropriate amount of stabilizer. It's a good idea to run the engine after doing this so the entire fuel system is exposed to the stabilizer. It's best to do this while underway so as to mix the stabilizer with the fuel (doesn't get much agitation at the dock
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