Do you think you have water in your gas tank and you want to get it out?
Then this article is for you. Water in the gas tank was probably a lot more common in older cars with rusty tanks and bad tank breathing. However, these problems do also appear in modern vehicles.
As you may know, your car won’t run on water unfortunately. So what happens when water is going into the engine?
In this article, I will try to answer all your questions about water in the gas tank — everything from the symptoms, causes and how to get it out.
Water in gas tank symptoms
As you may understand already, the fuel enters the engine and the combustion chamber, where the spark plug ignites the fuel mix. The air and fuel will create an explosion which will crank the crankshaft and enable your engine run to move your car forward. So, what will happen if there is water entering the combustion chamber instead of fuel? There will be a weak explosion or no explosion at all when the spark plug is trying to ignite it.
Here are the most common symptoms when it comes to water in the gas tank.
1. Rough acceleration
Rough acceleration is a common sign when it comes to water in the gas tank. Because the water is tricking the sensors that pick up the air-fuel mixture like the O2, MAF, and intake air temperature sensor, the air-fuel mixture will jump up and down and cause rough acceleration.
Due to the issues we talked about earlier about what will happen when the water enters the combustion chamber, you will probably also notice misfires when the water goes into the combustion chamber of the cylinder.
3. Rough idle
Rough idle is also a common symptom because of the faulty air-fuel mixture and the misfires. The car engine is susceptible at idle for minor mistakes, and it’s at the idle you will notice the most symptoms of water in the gas tank.
4. Check engine light
Modern cars have full-time monitoring of all the different car sensors of the engine. If one sensor is getting faulty values, it will send the information to the engine control unit, which will store a trouble code in the memory and sometimes it will light up the engine light if the problem is serious.
5. Steam from the exhaust
When you have water in the combustion chamber or the exhaust pipe, it will evaporate, causing steam. We all probably know what happens if you cook water over 100c – It will evaporate to steam. So if you notice that there is a lot more steam than usual from the exhaust pipe, it could be water in the gas tank causing it.
6. Slow acceleration
All the different sensors in the car are making sure that the air-fuel mixture is at a perfect mix all the time. If there’s water going through the engine, the sensors will get a faulty reading and may cause the engine to run too rich or too lean. This can cause the engine’s power to get reduced, and you may see symptoms like slow acceleration.
7. Hard starting condition
The start-up moment for any car engine is very critical. The fuel mixture has to be close to perfect or the spark plugs will not have enough fuel to ignite the fuel, or it will get drowned, and they will not be able to create an ignition at all. If you have water in the gas tank, it’s horrible for the starting condition, and you may have a hard time to start it. If you notice long cranking times, you may want to check this.
8. The engine does not start at all
You can have so much water in the fuel that the engine will not ignite at all. There is also a possibility that your engine is hydro-locked if it won’t even crank. Water can’t get compressed like air, and when the pistons are trying to compress the air in the cylinder, it will try to compress the water, which is not possible. This will cause the engine to lock up entirely and may even damage the internals of the engine like the crankshaft rods. This is not very common, and there has to be a lot of water in the chamber to make this happen.
If you think this is the case, unscrew one spark plug to make sure it’s possible to crank the crankshaft after that.
9. The problems appear after the car has been standing for a while
Fuel floats on top on the water and the water will stay at the bottom of the fuel tank when the vehicle has been standing for some time. When the fuel pump is pumping the fuel and water is mixed, if the vehicle has been standing for a while, the water will be in the bottom of the tank. Most fuel pumps suck the fuel from the bottom of the tank and what will happen if the car has been running for a while? – Yes, the fuel pump will only pump water to the engine.
Causes of water in the fuel tank
So now you know the most common symptoms of water in the gas tank, but how do they happen from the beginning? Well, there are a few possible causes of water in the gas tank. Here are the most common issues that you should check if you notice them in your car.
1. Tank cap is leaking/tank leak on top
If your tank cap is leaking and not sealing correctly, there could be water running into the tank, and it could also be caused by condensing because of that. Make sure that your tank cap is sealed and tightened correctly. On older cars with a steel tank, there could also be rust-holes on the top of the fuel tank which would cause the water to stream down into it. Newer cars use plastic fuel tanks, so this is not very common on these if there is no damage on the top of the fuel tank, which is very unlikely.
2. Bad tank breathing (EVAP)
If your EVAP (evaporative control system) is not working correctly or leaking, it could cause condensation to enter the fuel tank. You have to check that the control valves for the EVAP system are in good condition and that there are no leaks in it. This is done in the best way with an EVAP smoke machine. Let a mechanic take a look at this if you are not sure what you should check.
Condensation can also enter the fuel tank after long periods without refilling the tank. We are talking about 10+ years without a refill that can cause this.
So you have checked the fuel tank cap, the fuel tank, and the EVAP system, and they’re in good condition, and you still have no idea where the water was coming from? Well, there may be someone that doesn’t like you and has filled your fuel tank with water to mess with you. If this is the case, go to the next steps of how to get the water out from the fuel tank.
How to get the water out of the gas tank
So now you know the symptoms and causes, and you are sure that you have water in your gas tank. Now it’s time to learn how you could get rid of it. There are some different solutions for this and here are some of the tips, based on how much water you have in the fuel tank.
1. Empty the tank and replace the fuel filter & refill
The best thing to do when you have water in the fuel tank is, of course, to empty the tank and refill it again with new fuel. This is often pretty time-consuming work, and you need some equipment. You need a vacuum machine to suck out all the water from the tank, so this job is better to leave to a mechanic workshop with these machines to do the work for you. You can also pump it out with the inbuilt fuel tank, but remember that the fuel pump is often fitted some millimeters up from the bottom of the tank and there is a chance that there will be water left on the bottom.
If you consider getting one of these machines, I can recommend this manual storage machine from Amazon: ARKSEN 30 Gallon Portable Fuel Transfer Can. You can also put this hose on the bottom of the tank and pump out the water from the bottom of the tank if the car has been standing for a while. Remember to replace the fuel filter after doing this.
2. Fill with a bit of methanol or special fuel additives
If you think that you have a small amount of water in the fuel tank, you can try to get it out either with methanol or using a special fuel additive for this purpose. Remember that this will not remove loads of water from the fuel tank and only works if you have a small amount. If you want to get one of these fuel additives, I can recommend this one from Amazon, and it’s very effective: STP All-Season Water Remover (5.25 fluid ounces).
Make sure to read the instructions carefully to ensure that you are not damaging the engine or other parts. If you want to try it with methanol, be very careful and only use small doses of methanol.
So in short, water in the fuel tank is terrible for the engine, and it can cause serious damage to your engine if you do not fix it as soon as possible. If you have any other questions about fuel in the gas tank or other car questions, you are welcome to leave a comment below. I will try to answer all questions as fast as possible!
Hello I’m Magnus, the owner and the writer of this website. I have been working with cars since I was 16 and I’m specialized with in-depth Automotive diagnostics. Also been driving drifting for the last 6 years. I’m here to give you answers to all your automotive questions and I hope that you enjoy our content.