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Help! There’s Water in My Gas Tank: What to Do Next

Do you have water in your gas tank? Do you suspect water in the fuel? If you suspect that there is water in your gas tank, you cannot put off addressing it. Fixing the issue helps avoid further damage and costly repairs. 

Today, we’ll take a look at how to determine if there is water in your fuel and guide you through the steps you should take in this frustrating situation. We’ll discuss what to look for, how to diagnose the problem, and how to remedy it. You and your vehicle should be back up and running before you know it.

Let’s dive in!

How Does Water Get in a Gas Tank?

There are several ways that H2O can get into your gas tank. The most common cause is condensation. It happens anytime the temperature outside changes rapidly. A layer of moisture forms inside the gas tank from the condensation of the air and can accumulate over multiple heating and cooling cycles. Enough moisture gathering can wreak havoc on your fuel system and engine.

Additionally, we’ve heard horror stories of issues from contaminated pumps. You may think you’re pumping gas into your tank, but it could contain water. These situations typically occur from damaged holding tanks after heavy rains. One Indiana gas station had contaminated pumps due to a small bolt coming loose. It may be rare, but it can happen!

Water can enter the system by driving through flooded areas or large puddles. Failing seals and gaskets can let water seep into the system. It can get sucked up and reach your tank. However, no matter how it enters the tank, it can cause damage.

Pro Tip: Time is running out for your to discover When Does Gas Expire and How to Make It Last?

What Happens if Water Gets in Your Gas Tank?

Small amounts of water and condensation can actually get absorbed in the fuel and burned. While many talk about the drawbacks of ethanol-free gasoline, it actually comes with some benefits. Ethanol in gasoline helps absorb water into the fuel so it can get burned. Diesel can also absorb water to some extent. While it’s never good to have water in your fuel, the major problems come in when the water content exceeds the saturation potential of the fuel. This causes our water to accumulate at the bottom of the tank because it’s heavier than the fuel.

Water in your tank can cause severe issues for you and your vehicle. A watery fuel mix can result in a lean mixture, causing the engine to run roughly or stall.  Additionally, H2O can cause corrosion and rust in the lines, injectors, and other system components. Clogs and other issues are common and can cause further damage to the engine.

One of the most severe consequences to water in the fuel tank is if pure water gets drawn into the fuel pump. Particularly in high-pressure, directly injected systems, these pumps have very little tolerance to water. Because water doesn’t compress like fuel, the pumps can see a catastrophic failure and brake components if even a small amount of pure H20 gets sucked in.

Failure to address the situation can also cause extensive damage to the engine and injectors. These are typically costly repairs and may even require an engine replacement. You’ll be out of money, and your vehicle will be out of commission for the foreseeable future.

removed diesel fuel tank from truck
We hope you don’t have to do this, but once upon a time, we had to remove our entire fuel tank to clean it out of contaminated fuel!

What is a Water in Fuel Warning On Dash

Some dashboard indicators can communicate a variety of information. Many diesel vehicles have warning lights to indicate the presence of water in the fuel filter. This light typically looks like a gas pump with raindrops next to it. However, it’s a good idea to check your owner’s manual to familiarize yourself with the lights specific to your dash.

Luckily, you don’t have to panic if this indicator light activates. Draining the fuel water separator is straightforward and only takes a few minutes. Just grab a jug or container and locate the drain. It’s typically a bright yellow cap under the vehicle near the tank. 

Place the container under the cap and twist the lid to open it. A mixture of fuel and water will drain from the separator and into the container. Since water is heavier than diesel, it will settle at the bottom of the container. Secure the cap once it finishes draining.

Pro Tip: Put on your myth busters cap and uncover True of False: Will Sugar in Gas Tank Ruin Your Engine?

water in fuel indication light on dash
All of our diesel vehicles have had a light or warning of water in the fuel.

Signs and Symptoms of Water in Gas Tank

You want to catch this situation as soon as possible. As a result, it’s a good idea to be aware of the signs and symptoms. Doing so can allow you to address the issue and limit damage. Thankfully, there are a handful of standard indicators that you can watch for with your vehicle.

The most obvious sign is a dashboard indicator light. It’s usually a specific indicator for alerting to moisture in the fuel filter. This sensor is not sensing water in your tank, but rather a special water separator catch before it makes it to the engine. These almost always have a drain at the bottom to drain out the water without taking the filter all apart. Sometimes there is even a clear view window so you can see the water and drain out the correct amount.

fuel water separator in a diesel engine with clear view and drain bowl
This is the fuel water separator in one of our diesel engines. It is clear so we can visibly look for water. While it will be almost the same color, you will see it separated out at the bottom of the bowl.

One of the most common symptoms to watch for when water in fuel is reaching the engine is rough idling. The water mixes with fuel and throws off its burn consistency. An improper mixture can result in poor performance, misfires, and unusual noises. Drivers may also experience issues starting their vehicles. These issues, however, can be from many different problems and not just water in the fuel.

You may also just suspect you have water in your fuel. You can confirm this with a fuel water test kit or a paste that you place on a rod and dip into the tank. The paste changes color if pure water is detected at the bottom.

Gasoila-WT25 Regular Water Finding Paste, 2.5 oz...
  • Reformulated for better consistency and improved color change
  • Quickly and accurately detects water in fuel storage tanks
  • Mustard yellow paste will turn red upon contact with water

Steps to Remove Water from Gas Tank

If you experience this issue with one of your vehicles, you must take action. These issues typically get worse and more expensive the longer you wait. Do yourself, your vehicle, and your bank account a favor and address them immediately.

Stop Driving the Vehicle

If you know you have water in your gas tank, you should first stop driving the vehicle. Continuing to use it will only make the issue worse or potentially cause lots of damage.

Drain the Fuel Tank or Water Seperator(pump)

If you got the water in the fuel light on the dash, it most likely means you just need to drain the separator reservoir. Your vehicle’s manual should have instructions on how to do this. Usually, it’s as simple as placing a cup under the separator and opening a valve. Watch the cup to see when the water quits flowing, and it turns to pure fuel.

If your fuel tank has too much water in the bottom, you will need to drain the tank. Very few tanks have drain plugs, so you will probably need to siphon out the fuel. Use a siphon or pump to transfer the liquids into a separate container. Depending on how much is in your tank, it may require multiple storage containers.

Once you’ve drained the tank, its good to inspect the inside. This can be done with an inspection camera or if the tank has been removed visually. Look for any signs of debris and rust. If the tank was removed, clean the tank thoroughly and use a tank cleaner for the best results. Doing so can help you avoid issues down the road.

fuel tank cleaner
Once upon a contaminated tank of fuel we had to remove our entire tank, drain and clean it out. We had good success with this tank cleaning kit.
Delphi FC01 Fuel Tank Cleaning Kit
  • New fuel tank cleaning kit removes growth in the tank, breaks...
  • Can extend the life of the new fuel sending unit by removing...
  • Delphi's low-suds cleaning solution is specifically designed to...

Replace the Fuel Filter

You now need to replace the fuel filter. Its job is to prevent debris and other gunk, including water, from entering your gas tank and system. However, the filter can’t function if water gathers on it. Replacing this device helps protect your system from any remaining bits of water and reduces the chances of further damage.

Unfortunately, replacing the filter will significantly depend on your vehicle. Ensure you know what you’re doing before removing any parts or pieces. When in doubt, leave it to a professional. You could end up costing yourself more money if you don’t.

Refill the Tank with Fresh Fuel

It’s time to refill the tank with fresh fuel. If your vehicle is gasoline, It’s a good idea to ensure your fuel contains 10% ethanol. Ethanol does a suitable job of absorbing moisture and helps eliminate any water or moisture remaining in the tank.

Once you fill the tank, start the engine and let it run for several minutes. Doing so allows the fuel to circulate throughout your system. Listen for strange noises and watch your dashboard for alerts or critical messages.

Pro Tip: While filling up, you’ll want to know Should You Put Ethanol Free Gas in Your Tank?

Refilling gas tank
Only refill your gas tank with fresh fuel after draining the tank and replacing the filter.

Add Fuel Water Remover If Cannot Get Ethanol Fuel

When ethanol fuel is unavailable, find a fuel water remover product at a local automotive store for your gas tank. This additive absorbs moisture in the system and can prevent damage to the engine or other components.

Select a product that is compatible with your vehicle and follow the instructions. Using too much or too little can cause issues or be ineffective. You’re wasting time and money if you do this incorrectly.

Once it’s in the tank, let the engine run for several minutes. During this time, the mixture flows throughout the system. Unfortunately, this isn’t an instantaneous fix, and it takes some time to do its job.

Hire a Professional If Symptoms Remain

If you have followed the steps but the symptoms persist, it may be time to hire a professional mechanic. A qualified mechanic has the knowledge, experience, and equipment to diagnose and repair these issues.

When hiring a mechanic, choose someone with experience working on your specific type of vehicle and system. Ask for recommendations from friends and family, or search online for reviews of local mechanics. Once you have found a mechanic you trust, communicate the symptoms you are experiencing and the steps you have already taken to address them.

A mechanic may need to perform additional diagnostic tests to determine the root cause of the problem. They may recommend extra repairs or replacements of components. Be sure to ask for an estimated cost of any repairs before authorizing the work.

Car mechanic
When in doubt, turning to a mechanic is the best way to ensure your vehicle is fixed quickly and correctly.

Preventing Getting Water in Your Gas Tank

Preventing water from entering the fuel system is critical. Never drive in water that gets past the fuel fill or fuel in heavy rain. External water sources are usually easy to avoid but sometimes may surprise you.

Keeping your gas tank full is another method to help minimize condensation. When your tank is empty or low, it creates more space for air and moisture to enter the tank. This can lead to condensation and water buildup. If you are not ging to use the vehicle for a while, store it with the fuel topped off. Also add stabilizer when storing.  

Lastly, for gasoline vehicles using fuel with ethanol in it will minimize water problems. Some choose to use ethanol-free fuel, but using it every so often can be beneficial. We use ethanol-free fuel all summer in our boat but store it each winter with a full tank of ethanol-free. Before doing this, we had water problems with the fuel, but no longer since using the ethanol fuel.

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Don’t Panic: Handle Water in Your Gas Tank

Water in your gas tank can be a frustrating and stressful situation. However, it’s important to remember that there are steps you can take to address the issue. Following the steps we’ve shared can resolve most minor situations. However, contact a mechanic if the symptoms persist. 

You can take control of the situation by staying calm and following these steps. You’ll make informed decisions and return to the road before you know it.

Do you have a trusted mechanic to contact if you experience issues related to water in your gas tank? Tell us in the comments!

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About Tom Morton

Tom, a Pacific Northwest native, is our technical genius. Born in Washington and raised in Alaska before settling in Michigan. He's the man who keeps our operation running, both figuratively and literally.

With a background in Electrical Engineering, Tom specializes in RV solar systems and lithium batteries. He made history as the first documented individual to use a Tesla battery module as an RV battery. Tom has personally assisted countless RVers with system installations and has educated thousands more through his videos and articles.

Cinematography is another of Tom's passions, showcased in his work on the Go North series. You can see his camera skills on display in The RVers TV show on Discovery Channel and PBS where he also stars as a co-host.

Tom's mechanical expertise extends beyond RVs to boats, planes, and all things mechanical. He's renowned for taking on maintenance and repair projects single-handedly and is often spotted underneath RVs, making him the technical backbone of our endeavors.

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