Water in a Gas Tank: What REALLY Happens?! (Explained)

Water can enter your car in so many ways. It can come from rain, from a simple splash, or even from extreme moisture. No matter where it came from, water in your gas tank is a significant problem that you must handle right away. Still, you may wonder:

When there is water in a gas tank, what really happens? When there is water in a gas tank, it can cause several issues that can result in significant damage to your vehicle. First, it can damage the fuel system and the engine in itself. For this reason, you need to address and resolve this issue as soon as possible.

Water in a gas tank causes problems not just in the cylinder, but it may also harm injectors if it swells quickly at the injector tip (because of the injector’s innate heat). And if it remains in your fuel system for a long time, it can create corrosion in your fuel system as well as a variety of other issues with your engine.

In this article, you’ll read a walk-through of all the possible effects of water in a gas tank. This way, you can understand all the risks involved, and you’ll know how to fix them if it ever occurs on your vehicle. 

So, without any further ado, let’s get into it!

Water in a Gas Tank

What Happens If You Put Water In a Gas Tank?

When there is water in the gas tank, it can cause your vehicle to buck, stall, or not start at all. Or, it can even make starting the car difficult. 

The reason is that the water and gasoline get separated while the automobile sits for a long time. When it happens, the water goes into the bottom while the fuel rises to the top.

The water can promote corrosion on the bottom and poor combustion if ever it reaches the engine. Further, the moisture it provides would turn into rust over time if left unchecked.

For this reason, you may experience several issues, such as trouble with acceleration and even with firing up the engine.

If you’re having difficulties trying to get up to highway speeds but nothing else appears to be wrong with your car, you should check for water in your tank.

You may also notice abrupt, unpredictable changes in speed that occur without your involvement. It might also seem like a stumble.

If your gas tank is complete, but your car still crackles when you step on the gas pedal, the gasoline may be contaminated with water.

What Do You Do If You Get Water In Your Gas Tank?

It’s a no-brainer that you need to remove the water in your gas tank, and here’s how you can do it.

In general, the best approach to eliminate all water from the tank is by draining and refilling your gas tank. For most drivers, this idea may appear to be a costly option. Still, the damage to your vehicle that you will save is well worth it.

You can consider using fuel additives such as HEET®. Products like these are designed to help remove water from the gas tank. Take note, though. While duel additives can effectively remove water from a gas tank, they won’t work well if your gas tank contains a lot of water.

If you cannot do this process independently, it is worth your time to hire a skilled technician. If not handled appropriately, water in a tank may cause expensive damage to a vehicle.

Will the Water In a Gas Tank Ruin an Engine?

Yes, water in your gas tank will most likely destroy or, at the very least seriously, damage your engine.

As mentioned earlier, the effects of water in a gas tank can be pretty devastating if you don’t resolve them immediately.

Even a tiny amount of water can cause moisture and fuel contamination. In addition, if you leave water in a gas tank for long periods, it can cause corrosion and lead to rust build-up.

Moreover, it can affect the performance of your engine in the long run. For this reason, you need to resolve it and remove the water in a gas tank as soon as possible.

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

Any vehicle’s engine can be harmed by a whole cup of water or even less. Although some water may easily make its way into gasoline tanks, much more than this may create significant difficulties for a vehicle.

In short, the more water you have in a gas tank means the more damage it can bring to your fuel system and even to the whole engine.

With this in mind, you may wonder how large amounts of water can take a toll on your vehicle. For instance, you may ask what will happen if you have a gallon of water in your tank.

A Gallon of Water in a Gas Tank – What Happens?

If you put a gallon of water in a gas tank, your vehicle won’t even start at all. In most cases, a gallon of water is too much for every car. In addition, it can lead your engine to stall at first if you have a fill of fuel inside.

However, if you have a gallon of water and you also have a small amount of fuel, it can be enough to disable your engine from starting.

Another thing to note is that this amount of water cannot resolve by adding a simple fuel additive. 

In most cases, you’ll need to take out the whole tank from the vehicle, drain it, dry it, and then refill it with gasoline.

It may seem like a lot of work, and it’s true. However, if you imagine prolonging the issue, you’ll have to deal with more work than that amount.

water in gas tank

How to Check for Water in the Gas Tank?

If you want to check for water in the gas tank, you’ll need to know the common signs of such an issue. Here are nine symptoms or issues that you can observe to know that your gas tank contains water.

Engine starting issues

There is a point when there is so much water in the gasoline that the engine will not even start. If your engine doesn’t even turn over, it may be hydro-locked. Water cannot be compressed in the same way that air can, therefore when the pistons try to control flow in the cylinder. They will also try to compress the water, which can happen.

It will cause the engine to completely lock up and even harm the internal components, such as the crankshaft rods. It’s unusual, and there must be a lot of water in the chamber for it to occur.

Issues when the car is idle

A bumpy idle is also a common symptom due to the inadequate air-fuel mix and misfires. The vehicle engine is prone to minor mistakes when idling, and it is during this time, you will observe the most symptoms of water in the gas tank.

Faulty acceleration

Slow acceleration is perhaps the most prevalent indicator of all water in gas tank symptoms. Since the engine mistook the water for fuel, the air-fuel combination in the combustion chamber will be odd.

All of the sensors in the automobile are constantly ensuring that the air-fuel combination is optimal.

If the engine is wet from the water, the sensors will give an incorrect reading, causing the engine to run excessively rich or too lean. The engine’s power may be diminished as a result, and you may notice symptoms such as sluggish acceleration.

Engine misfires

You will most likely notice glitches when the water reaches the cylinder’s combustion chamber because of the difficulties we discussed when the water reaches the combustion chamber.

Misfires and harsh acceleration are two symptoms that are often confused since misfires may cause bumpy acceleration, but misfires can also be seen while driving.

Steam releasing from the exhaust

When water evaporates in the combustion chamber or the exhaust pipe, the engine will start releasing steam. We all know what happens when you boil water over 100 degrees Fahrenheit: it turns to steam.

If you observe a lot more steam coming out of the exhaust pipe than usual, it might be due to water in the gas tank.

Engine lights blinking

All of the engine sensors in vehicles today are monitored in real-time. Suppose one of the sensors detects incorrect readings. In that case, it will communicate the information to the engine management unit, which will record a trouble code in memory and, if the situation is complex, may illuminate the engine light.


In a nutshell, water can mean a disaster for every vehicle owner. When a gas tank contains water, it can cause several problems, some of which might cause serious harm to your car. Water has the potential to harm the fuel system as well as the engine itself. As a result, you must identify and fix this problem as quickly as feasible.

Thus, it’s a no-brainer that you need to fix such an issue as soon as possible and do your best to avoid water from entering your gas tank. Such things can help save you from the hassle of dealing with all the issues it can bring.



Image credits – Canva

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My name is Hank, and I've been in the automotive industry for 27 years. I've been working in my own auto repair shop for the last 13 years, and now I want to help you here, on my blog. Let me know if you have any questions. Read more