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water in the gas tank

How can you tell if you have water in your gas tank, and what do you do about it?


  • edited July 2008
    You need to take a sample out of the tank and see if the water phase seperates out of the gasoline. To remove moisture from the tank, the isoprophyl alcohol in SeaFoam will absorb moisture from the tank so it can be carried into the engine and be vaporized.

  • edited July 2008
    In the extreme, remove the gas from the tank,pour it into another tank that has a drain on the lowest point open the drain and let it flow into a clear container (small diameter say 8 inches high) and see if this sample shows a gas water mixture. What to do with it,seperate the gas water mixture and put the gas back in the tank.(keep draining till only gas comes out)
  • edited July 2008
    Year, make, model please..
  • edited July 2008
    A small amount of water in the gas tank is common, especially if your gas tank is usually half full or less. This is due to condensation, and is really nothing to worry about.

    If you have LOTS of water is your tank, you will know it because your engine will buck, stall, and otherwise not run correctly, since water cannot be burned in the engine as a fuel (despite the many claims to the contrary). It is "possible" to get this much water in your tank, but it happens very rarely, and only under abnormal circumstances. It would be very unusual for you to have a harmful amount of water in your tank. Not impossible, but unlikely.

    If you think you have more than a tiny amount of water in your tank, you can purchase a bottle of Dri-Gas, or a similar product (there are many), at an auto parts store, or even at your local grocery store. These products will absorb any small amounts of water in the tank and eliminate them. I usually use such a product once or twice a year, especially right before winter sets in, to avoid fuel line freezing. It's probably unnecessary, but I once had a frozen fuel line, and I don't want to have one again.

    Is there a reason you suspect water in your gas tank?
  • edited July 2008
    McP, a couple of points. There is never any "condensation" in modern gas tanks. They are sealed and pressurized. All venting is out-gassing through the carbon canister..Todays fuel contains 10% ethanol..If ANY appreciable amount of water contaminates the fuel, the whole mess separates, "phase separation" I think they call it...It must then be drained from the tank. Today, because of the ethanol, Marinas are plagued with this problem because of the poorly sealed marine gas tanks and leaky deck fittings..
  • edited July 2008
    "Water in the gas" is a common scapegoat excuse when someone has no clue what the actual problem is though.

    Details on the car and symptoms might help.
  • edited July 2008
    I agree, although I was not aware of the lack of condensation in modern fuel tanks. Thanks for the info. I never doubt what you say, Caddyman.

    The ethanol which we cannot escape renders water in the gas tank almost a moot point. I was just trying to make the OP feel more comfortable, and I hoped to find out why she thought there was water in her tank in the first place.

    I'd still like to know.
  • edited July 2008

    As usual, I agree with OK4450. In my experience, a bad mechanic will frequently fall back on the old "water in the gas" excuse if he doesn't really know what the problem is. And, all too often, friends and co-workers will automatically list that as one source of a car problem--no matter how irrelevant it may be. (The other automatic response, no matter what the problem may be is, "you need a new battery")

    Water in the gas can be a major problem--when it really exists. However, it is less likely than those well-meaning friends would have you believe.
  • edited July 2008
    I agree that water in the gas tank is just an excuse for not being able to diagnose real causes (except perhaps in New Orleans cars), but I did want to comment on the question of condensation. Condensation comes in with the outside air as the gas gets lower and the tank breaths in. The charcoal bed being carbon, and the gas fumes being hydrocarbon, the bed will catch gas molecules (carbon bonds to carbon really well) but it doesn't catch moisture.

    Warmer, moisture-laden air will deposit the moisture if it comes in contact with cooler metal surfaces that transmit heat well such as the insides of gas tanks. Condensation stil happens in modern tanks, however it isn't the problem it used to be because (1) of the ethanol and (2) because fuel systems now are high pressure lines all the way to the injectors, so moisture can't condense on the inner surfaces of the fuel system and freeze up.

    The net result is that I wholeheartedly agree that "water in the gas" is rarely more than an excuse and condesation in the tank is no longer a problem, but condensation does still happen in the tank.
  • edited July 2008
    Since most gas contains ethanol, how come it doesn't scavenge the water like a bottle of dri-gas does?
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