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Condensation in Fuel Tanks

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  • Condensation in Fuel Tanks

    I've always hear of this concept, however, never really understood the science behind it. I never had a problem with it either. What I do know is, in order for water to condense from the air it most reach it's dewpoint temperature. The dewpoint is always less than the ambiant air temperature, even if the relative humidity is 99.9%.

    So knowing that, the fuel tank wall would have to drop below the ambiant air temperature down to the dewpoint level. How would this happen?

    Spoiled One should know. He's a science type guy.
    We never really grow up, we only learn
    how to act in public

  • #2
    All it takes is for the fuel to be colder than the air from the night before. Just look at the outside of your beer mug after pouring a cold one on a hot day.
    "I'd rather be fishing!"


    • #3
      Well Doug, in order to condense water out of the atmosphere a surface must be much colder than the air. In theory this could happen when it is very cold at night and warms up rapidly during the day, but there isn't enough air volume within a tank to hold much vapor IMHO. If you leave your tanks full, this volume is reduced to next to nothing. If you are getting water in any real measurable quantity I suspect that it is coming from somewhere else, but I am not an expert. I have stayed in a Holiday Inn Express, though.

      I removed exactly five gallons of "condensation" from one of my 135 gallon tanks my first season with the current boat. It wasn't coming from the airspace in the tank, but from the asshat teenager that lived down the street. Karma is a real mother. Two days later that speeding punk wrapped his little mustang around a light pole. Fortunately he suffered no bodily injury. He just had a bruised ego. We moved from that neighborhood and I have not had any more water problems. I do watch my racor as I head out of Passage Canal each trip. I might get a tablespoon of condensation.
      sigpicSpending my kids' inheritance with them, one adventure at a time.


      • #4
        Not to mention ALL fuel comes from the pump with moisture in it , all of it , Diesel, Gas, Jet Fuel , all of it and fuel being lighter than water [ that specific gravity thing ] the water sits under the fuel on the bottom of your tank until enough water builds up to hit the pickup tube in your fuel tank and BINGO, you be sucking water .

        Then you add condensation and butthead neighbors and KAPOW you be having a water problem . Racor filters are our friends just remember to carry SPARES ON THE BOAT and a FILTER WRENCH to change it/them .


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