[Fr. Frank]

Tucker's post reminded me of another possibility. If your tank is old and bedded in foam, you could have crevice corrosion that is allowing water to enter the tank. If this is the case, you will likely also have gas, or at least the smell of gas in your bilge. I had pin holes caused by corrosion in the tank in my action craft. The first symptoms were the smell of gas (but no liquid fuel) in the bilge, and water in the gas. Dave

Most likely the primary culprit is the fuel has water in it when you put it in your tank. However, as you can read above, it may not be the only problem. I use Marine formula Stabil in my fuel, AND I buy Ethanol-free gasoline, AND I use a 10 micron Racor water separating fuel filter with a visible resevoir to drain water, AND I keep my fuel tank topped off after every use.

I read on the Hull Truth a 7-8 years back where a rep from a fuel tank manufacturer in Florida (RDS?) stated that their testing showed that here in Florida, a half-full 100 gallon Aluminum marine fuel tank in an uncovered and trailered boat could accumulate from 1-3 GALLONS (not quarts) of water per month just from condensation. The 1 gallon was the MINIMUM condensate accumulation in a month.

He suggested the only way to truly minimize that condensation was to keep the tank as full as possible, and that covering the boat (or parking it under a cover) to minimize heating and cooling of the tank was a good idea as well. He also said that fuel/water separators were a must and additives were also a good idea, although he didn't recommend one over another.

I got a new fuel tank in '04 from RDS, and the lack of a "well maintained" water-separating fuel filter will void my 10yr warranty on it.