What Happens If Water Gets in Your Gas Tank?

Most people are aware that you should only put gas in your gas tank, but not everyone knows precisely what happens if other things, such as water, gets in a gas tank. It can lead to specific symptoms and problems, which tell you when this occurs by accident. What happens if water gets in your gas tank?

If water gets in your gas tank, it’ll degrade the components of your engine. This includes the fuel injector, gas tank, fuel pump, fuel filter, and eventually the entire engine. Water will rust metal parts, destroy electronic components like fuel injectors, and stop the engine from working.

In this article, I’ll be covering what happens if water gets in your gas tank, how to tell if water is in your gas tank, and what to do about water in a gas tank.

Symptoms of water in your gas tank.

Why Water in Your Gas Tank is a Problem

Water can get in your gas tank for various reasons, and you may not always immediately notice when it happens.

For example, you may have left your gas cap off by accident before it rained for a while, a car may have been sitting outdoors for a while, or perhaps a dodgy gas station filled your tank with gas and water. Regardless of how the water got there, the problem occurs once it’s in your gas tank.

How Engines Work

To understand why water is bad for engines, you’ll first need to know how engines work.

In order to operate, an engine has to push the fuel from the gas tank to the engine, where it combusts. This combustion physically moves the engine’s pistons, which, in turn, move the crankshaft.

There’s more to it, as this page from the Department of Energy shows, but the important part you need to understand is that fuel is burned to power the engine.

Small amounts of water in a fuel tank are normal, and even gas has a tiny amount of water in it, but water usually makes up far less than 1% of gas. Tiny drops of condensation can be shed from fuel caps, and not keeping your gas tank full can induce condensation. Areas with high humidity or temperature fluctuations are especially prone to producing this kind of condensation.

However, if there’s too much water in your gas tank, you’ll start to see problems.

What Happens if There Is Too Much Water in a Gas Tank?

The problem with too much water in a gas tank is simple, as water doesn’t combust like fuel does, and it certainly can’t power an engine the way gas or other fuel does.

If there is too much water in the gas tank, engines sputter, or otherwise refuse to work. If you ignore the issue, the water can get into the engine and fuel injectors, where it can wreak havoc.

Water in your fuel system is bad news because water has a nasty tendency to rust metal and cause sensitive electronics, like those in your injectors, to fail. Fuel injectors lose their ability to determine how much fuel to push to your engine to run, causing the engine not to work.

Water in the fuel also causes the sensors to misread the fuel. It could misread the fuel mixture as too rich, which means too much fuel, or too lean, which means it has too much air.

What Happens When Water Sits in the Gas Tank?

When water sits in the gas tank, it can lead to rusting, and a large amount can destroy an electric fuel pump if it is fully submerged in water. It can also clog up your fuel filter, which is specifically meant to handle fuel.

Sensors misreading the fuel-air mixture entering your engine most notably cause sputtering, sudden performance changes (from sputtering to roaring engines), and general rough performance.

Again, if water is left too long, misreading the fuel will progress into fuel injectors straight-up failing.

If you suspect that any significant amount of water has gotten into your gas tank, you must address the issue immediately. If you ignore it, the price for repairs will only climb over time.

Symptoms of Water in Your Gas Tank

Water in your gas tank will cause specific symptoms to occur, and the severity of these symptoms depends heavily on how much water’s there. The general signs remain the same, however.

Some symptoms to keep your eye out for include:

  • Sputtering when you try to start the engine, especially immediately after filling up.
  • The engine stalling completely, especially right after refueling the tank.
  • Jolting as the engine alternately tries to combust fuel, then water, or vice versa.
  • White smoke issuing from your exhaust, caused by the engine turning water to steam.
  • The engine refusing to start at all. This is because the water interferes with the engine’s needed rich fuel-air mixture.
  • The check engine light turning on, often after refueling or starting the engine for the first time that day.

How Much Water in A Gas Tank Will Ruin A Car?

There’s no definitive answer for how much water in your gas tank is too much. That said, as little as one cup of water in your gas tank can cause serious problems, and any more than that will definitely be noticeable. If over a cup of water gets into the gas tank, your car will probably not work.

The good news is that in most cases, water in your gas tank won’t immediately ruin the engine. The bigger problem is ignoring the issue rather than the water itself because letting it sit in your engine and corroding its components is the main way it causes damage.

How to Check for Water in Your Gas Tank

To tell if water is in your fuel tank, check for the presence of the above-listed symptoms. Follow these steps to see if water is in your tank:

  1. Find the low point of your fuel tank and drain it. You need the low point because water is denser than gas and sinks quickly after it gets into the tank.
  2. Open the drain and collect the fluid that comes out. You’ll be able to instantly tell the difference between water and gas as the water will settle to the bottom, as gas and water don’t mix.

If you find water in your gas tank, you’ll need to take some additional steps to completely rid it of water. If you don’t and the water stays in there, it can and will quickly degrade and destroy your engine.

How to Remove Water in Your Gas Tank

There are a few ways to remove water from your gas tank, depending on how much is in there.

If it’s only a small amount of water, there are certain additives you can pour into the gas tank to get the water out. If there’s a lot of water in the tank, though, the whole tank should be drained to be certain it gets out.

Let’s take a look at the two methods you can use to remove water from your gas tank.

Additive Method

Some people think that rubbing alcohol is a suitable additive to remove water from gas tanks, but you should absolutely not use it. Rubbing alcohol has water in it already and has no way to actually get the water out of the gas tank.

Instead, I recommend using a water remover product like ISO-HEET Water Remover from Amazon. This product is five times more absorbent than regular gas dryers.

Of course, you don’t have to use this product in particular, but you should only use a reputable water remover product and not a home remedy. These products are often advertised as fuel line or fuel injector cleaners.

To remove water with water remover, you will need to:

  1. Add the entire bottle to the gas tank before or after refueling the tank.
  2. Drive as usual.

For small amounts of water, ISO-HEET or similar products will remove water from your fuel tank and lines before it can cause any problematic damage. However, for larger amounts of water, it won’t do much good.

Drainage Method

Draining a gas tank is the best and most surefire way of removing water before it can corrode and damage the engine. It may be difficult in some cases, but it’s always worth doing. Would you rather drain the tank or rebuild the engine?

Some people opt to try siphoning the tank, but this is a challenging task that poses a fire hazard and isn’t guaranteed to work, which is why I don’t advise trying it.

The exact steps for this method depend on whether your gas tank has a drain or not. If so, the step is as simple as opening the drain and collecting what comes out.

If not, the process gets more complicated.

To drain a fuel tank without a drain, you will have to:

  1. Remove the fuel tank. The exact steps vary based on your vehicle’s make and model.
  2. Drain the fuel tank manually.
  3. Replace the fuel filter. While it may have been damaged yet, it’s better to be safe rather than sorry.
  4. Pour fuel cleaner into the gas tank with fresh gas.
  5. Run the engine for 30 minutes to flush the fuel lines.

Final Thoughts

Water in a gas tank can be a major issue and cause significant amounts of damage. However, there are obvious signs that signal its presence. If you think you have water in your gas tank, use a fuel additive or fully drain the tank to get it out, depending on how much water is in there.




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