5 Symptoms of Water in a Gas Tank (and How to Fix)

It should be pretty obvious that water in fuel is a significant problem. How would you know if someone put water in your gas tank?

How do you know if you received a tank of bad gas? Or if there’s water in diesel fuel? We’ll answer these questions (and a few more) in this article.

See Also: 13 Ways to Get Better Gas Mileage (and Save Money)

What Happens if Water Gets in Your Gas Tank?

Gas and water don’t mix, and your car can’t run on water. Water in fuel will cause jolting and sputtering among other issues. The symptoms will always be worst when accelerating (when more fuel is needed). 

Top 5 Water in Gas Tank Symptoms

The symptoms of water in a gas tank can mimic other issues and be overlooked. Typically, you’ll find these common signs of water in the gas tank:

1) Performance Issues

car won't accelerate

When accelerating, the car will sputter or hesitate. The more you step on the accelerator pedal, the more noticeable it will be.

The reason for this is that the water in the fuel is tricking sensors such as the MAF by making them think a certain amount of fuel is entering the combustion chamber. In reality, only some of the liquid is actual fuel with the rest being water. This messes with the air/fuel mixture resulting in what is actually a “running lean” condition.

2) Your Car’s Performance Changes Overnight

Literally. It will run perfectly today and tomorrow, and then when it starts drawing on the water, it won’t run at all. You may notice a difference when first starting up but it’ll be most apparent when driving and accelerating.

3) White Smoke From Exhaust

white smoke from exhaust

Because water is entering the combustion chamber or the exhaust system, it will naturally evaporate and cause steam. This will make it appear that there is a good amount of white smoke coming out of your tailpipe.

Don’t confuse this with the slight white smoke you may see when you start up your car on a cold morning. With water in your gas, it will be more noticeable.

4) Hard to Start (or Will Not Start at All)

Like when accelerating, your engine requires a rich air/fuel ratio when you start your vehicle, meaning more fuel is required. This causes a water and fuel mixture to be more apparent.

If the spark plugs don’t get enough fuel to ignite it, it make take them a few seconds for a successful ignition. This will make it so your car is very hard to start. It’s possible that there is so much water in the fuel that your car will simply be impossible to start up.

5) Check Engine Light

check engine light

Like a lot of other issues that depend on accurate sensor readings, the sensor in question (whether it be the mass airflow sensor, intake air temperature sensor, or oxygen sensor) relays that information to the vehicles ECU.

If the ECU decides the information from the sensor is not correct, it will trigger a trouble code to be stored. This in turn will cause the Check Engine light to illuminate in your instrument cluster. By using an OBD2 scanner, you can confirm the issue to see if it’s related to a possible improper fuel mixture.

How to Get Water Out of Your Gas Tank

how to get water out of gas tank

You can find an additive to remove water from the fuel. Iso-Heet is probably the best water remover on the market today but there are others. These products are effective up to a point. If there’s more gas than water, they’ll work reasonably well. If not, they are ineffective.

We recommend draining the tank completely to be on the safe side. We’ll even give you the step-by-step instructions if you have mechanical experience but for most people, letting the pros handle it is the best option.

See Also: How to Properly Dispose of Old Gas

Step 1 – Drain the Gas Tank

Set aside an afternoon and drain your gas tank completely. Gas has a lower density than water, so it stays on top. The water should drain out first.

Some people would recommend waiting until you see fuel emerge. We don’t. You might save a few bucks, but it’s not worth the damage it might do to your car.

Allow the fuel to drain for a long time, though. You want to get out every bit of water as possible.

If your tank doesn’t have a draining feature, you’ll have to do things the old-fashioned way. It could be removing the tank and emptying it, or siphoning out the gas. Be careful. Gasoline is flammable.

Step 2 – Replace the Fuel Filter

Get a new fuel filter and replace the old one. Water might have damaged the fuel filter, causing it to disintegrate or weaken, which can render the fuel filter ineffective. More debris and dirt would be able to enter the engine, which causes further problems.

Would you rather spring some cash for a new filter, or rebuild the engine? Replacing the filter is a far safer solution.

Step 3 – Flush Fuel Lines

Flush the fuel lines. These are meant to conduct gas, not water. If water gets in, the lines will start to corrode.

It could result in a small leak that might be difficult to notice, but there would be a reduction in fuel economy and a real danger of starting a fire.

If you don’t know how to do this properly, take it to your mechanic. It’s a quick job and shouldn’t cost the earth.

Step 4 – Fill Up Gas Tank

Fill her up, and you’re ready to go. Now all that’s left is to put new fuel in, and you’re all set.

Avoiding the Problem in Future

Unfortunately, there are some gas stations out there who want to make a fast buck. They get away with it because this issue can go undiagnosed for a while. It’s also hard to prove that the station was the culprit.

These stations might water down the gas to save money or buy it from a cheap or disreputable supplier. If the gas price you’re paying seems to be too good to be true, it may well be contaminated.

We recommend finding a good station and sticking to it. Be careful if you are in a strange new area. Ask someone that you trust for advice on where to get the best quality gas.

In addition, if your car doesn’t have a locking gas cap, you may want to upgrade to one. There are people out there that have nothing better to do than sabotage your car no matter if they have a bone to pick with you or are just have bad intentions.  

Does Gasoline Float on Water?

Yes, it does. The liquids have different densities. The fuel will rise to the top, and the water will sink to the bottom.

The fuel system draws gas from the bottom, which means that the water will be drawn through first. It’s why you’ll experience problems quickly.

Should I Drive My Car in This Condition?

It’s another difficult one to answer. If you’re taking it a short trip such as back home or to a repair shop, it should be okay. Keep in mind that the vehicle needs fuel to power it, though, so if it gets water instead, it won’t have enough energy to move.

Worse still, the fuel system is not designed to handle water. The gas and oil lubricate the internal mechanisms of your vehicle. Introducing water into the mix can cause issues with lines rusting or more serious consequences, like friction.

Those parts grind against each other as part of their standard function, which is fine as long as the parts are adequately lubricated. Water can upset the delicate balance.

Should you drive your car? No, you shouldn’t. It might make a short run to the mechanic, but until the whole system is flushed out, you risk significant damage to your vehicle by driving it.


8 thoughts on “5 Symptoms of Water in a Gas Tank (and How to Fix)”

  1. Are you saying that the engine won’t run smoothly because not enough petrol can get through? Or that water is in the engine?

    How can water pass through a fuel filter?

      • Retro-fitting a fuel/water separator such as those found in diesel powered vehicles is costly and not as practical as one might think.

  2. Thanks for this article. A disgruntled employee did this to my truck and then stole the company truck he was driving and left me with nothing to drive and no way to work.


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