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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?

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.


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)

Year, make, model please…

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?

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…

“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.

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.

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.

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.

Since most gas contains ethanol, how come it doesn’t scavenge the water like a bottle of dri-gas does?

Ethanol doesn’t acavange water. Nor does dry gas. What it does is break down the surface tension to allow the water to disperse itself in the gas when agitated. It has no effect whatsoever on moisture suspended in the air.

I thought it was a cosolvent; alchohols are soluble both in gasoline and water. OK, so why doesn’t ethanol in gas allow water to disperse, then?

Maybe there’s not enough. If the alcohol already dipsersed in the gasoline there might not be enough left over to dissolve the water, too. I agree that ethanol should dissolve any water in the tank and both (together) would mix with gasoline. I would not be at all surprised of dri-gas is alcohol.

Yeah, dri-gas is either methanol or isopropyl alchohol.

The car chugs a bit when running, not all the time but only sometimes. I’ve put stuff in the gas tank to absorb the water and it works ok for awhile, then the chugging starts up again. It doesn’t last very long, and again, only happens periodically. Any suggestions would be welcome.

There was a recent article on CNN’s website about lowlifes who rent a truck and return it with the gas tank filled with water instead of gas. I had to wonder how the truck doesn’t stall out almost immediately, and how the rental agencies are unable to go after the renter (press charges of vandalism). That aside, unless you’ve got a hole in the system letting in water, or someone is pouring it in the tank, or you got a load of really bad gas, the amount should be trivial and can be handled by the engine.

Has someone actually told you there was water in the tank or are you simply assuming this is the case based on the symptoms and what you’ve heard in the past about contaminated gasoline?

Your first step should be getting the codes pulled. Go to a local AutoZone, Advance Auto, Checkers, etc. and have them do this for you. It only takes a couple of minutes and it’s absolutely free. Post any results back here for disucssion.
My feeling is that you’re going to find out there is no substance to the water in the gas theory.

What if I, say, left the lid to the gas tank off and the gas tank door open then used a drive through car wash? I’m guessing quite a bit of water and soap entered the gas tank…

Help please. Strange as this may be, I actually did this yesterday. Went to the station for gas and a car wash. Opened my tank, took off the nozzle then decided against the gas when I realized I couldn’t use my gas card because there was no card reader on the pump. Replaced nozzle, went into the station to get my car wash codes and proceeded to get a wash with the lid open and the cap off. Then drove to another station where I discovered the error of my ways and I then added 15 gallons of fresh gas. Now what do I do??? Drive my other car to get some Dri-Gas? Take the car somewhere and have them remove all the gas? Since my tank was very low to start out with I could be in trouble already if water entered the gas line. It ran fine the short distance home.

Thanks for any advice.