Water in your fuel tank is a serious problem that can leave you stranded and facing expensive repairs. How would you know if someone put water in your gas tank? What if you received a bad tank of gas or diesel?
Let’s look at the most common signs of water contamination, what it’s going to cost to fix, and what the process of getting water out of your gas tank entails.
See Also: 13 Ways to Get Better Gas Mileage (and Save Money)
What Happens if Water Gets in Your Gas Tank? (Symptoms)
Simply put, gas and water don’t mix, and your car can’t run on water. When water contaminates your fuel system, it disrupts the combustion process, leading to various performance problems.
Here are the most common symptoms of water in a gas tank. Because they can mimic other issues, this cause is often overlooked.
1) Performance Issues
When accelerating, your car will sputter or hesitate. The more you step on the accelerator pedal, the more noticeable it will be since the fuel demand is greater.
This happens because water disrupts the combustion process. While sensors like the MAF sensor detect a certain amount of liquid entering the combustion chamber, only some of it is actual fuel with the rest being water. This creates an improper air/fuel mixture, effectively causing a “running lean” condition.
2) Your Car’s Performance Changes Overnight
Literally. It will run perfectly today, and then tomorrow when it starts drawing on the water-contaminated fuel, it won’t run properly. You may notice a difference when first starting up but it’ll be most apparent when driving and accelerating.
This sudden change occurs because fuel and water separate when your car sits overnight, with water settling to the bottom of the tank. Since your fuel pickup is located at the bottom, your engine initially draws the water-heavy mixture when you start driving again.
What’s particularly confusing for many drivers is how their vehicle can run fine one moment and struggle the next. This inconsistency is actually one of the biggest giveaways that it’s a water contamination issue rather than a mechanical one.
3) White Smoke From Exhaust
Because water is entering the combustion chamber or the exhaust system, it will naturally evaporate and cause steam. This can cause a good amount of white smoke coming from your exhaust.
Don’t confuse this with the slight white smoke you may see when you start your car on a cold morning. With water in your gas, it will be more noticeable and persistent.
4) Hard to Start (or Won’t 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 makes water contamination more apparent during startup.
If the spark plugs don’t get enough fuel to ignite, it may take them a few seconds for a successful ignition. This will make your car very hard to start. With significant water contamination, your car may simply be impossible to start.
5) Check Engine Light
Like a lot of other issues that depend on accurate sensor readings, water contamination can cause inaccurate readings from multiple sensors, including the mass airflow sensor, intake air temperature sensor, or oxygen sensors to be relayed your vehicle’s computer (ECU).
If the ECU determines the information from the sensors is incorrect, 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 if the issue is related to an improper fuel mixture.
6) Engine Misfires
Water in your fuel can cause specific cylinders to misfire. You’ll notice a jerking sensation, especially during acceleration, as individual cylinders fail to combust properly. These misfires happen when water reaches the combustion chamber instead of fuel.
7) Rough Idle
Even when your car is parked and idling, water contamination can cause noticeable roughness. The engine may shake, vibrate, or occasionally stumble as it tries to run on a compromised fuel supply. This again occurs because the water in the fuel disrupts the proper combustion needed for a smooth, steady idle.
Cost of Repairs
Most professional mechanics will charge somewhere between $300-800 for a complete fuel system drain and flush if there’s no extended damage (depending on your vehicle’s make/model and where you have it services.
It’s not necessarily cheap but much cheaper than repairing engine components damaged by long-term water exposure. The key is to catch and address the problem early on before additional fuel system components are affected.
If the water contamination has caused more extensive damage, you might face these additional repair costs:
Professional Repairs (Additional Costs)
- Fuel injector cleaning/replacement: $350-1,200
- Replacing fuel pump (if damaged): $300-1,000
- Fuel pressure regulator replacement: $150-500
- Spark plug replacement (if fouled): $100-300
- Worst-case scenario (engine damage repair): $1,500-4,000+
DIY Solutions
- Fuel additives: $5-15 per bottle
- Basic fuel filter replacement: $15-30 for parts
- Fuel tank drainage supplies: $20-50
How to Get Water Out of Your Gas Tank
For minor water contamination, fuel additives can be effective. Products like Iso-Heet are designed to bond with water molecules and allow them to safely burn through your engine. These additives work well when there’s a small amount of water relative to the fuel, but for significant contamination, they’re useless.
For more serious water contamination, professional help is typically necessary. Here’s what the process usually involves:
See Also: How to Properly Dispose of Old Gas
Option 1 – Professional Fuel System Service
For most modern vehicles, the recommended approach is to have a professional mechanic:
- Remove the fuel pump access panel (usually under the rear seat or in the trunk)
- Use a specialized extraction pump to remove the contaminated fuel
- Remove and clean or replace the fuel filter
- Possibly remove the fuel sending unit to access and clean the tank interior
- Replace any damaged components
- Add fresh fuel and fuel system treatment
Option 2 – DIY Approach (For Those with Experience)
If you have mechanical experience, you might be able to remove contaminated fuel yourself, though it’s more complex than in older vehicles:
- Locate your fuel pump access panel (check your owner’s manual for location)
- Disconnect the battery before beginning any work
- Use a siphon pump or extraction tool to remove the contaminated fuel (ensure proper disposal)
- Replace the fuel filter
- Add fresh fuel with a water-removing additive
For serious contamination, consider these additional steps:
Follow-up Maintenance
- Replace the fuel filter again after 1,000 miles
- Consider having fuel injectors professionally cleaned
- Keep a close eye on engine performance
- Have a mechanic check for signs of corrosion in the fuel system
Common Causes of Water in Your Gas Tank
Understanding how water enters your fuel system can help prevent future problems:
- Contaminated Fuel from Gas Stations: Some gas stations don’t properly maintain their underground storage tanks, allowing water to seep in. Heavy rains can sometimes infiltrate older or poorly maintained tanks.
- Condensation: Natural condensation occurs in partially filled gas tanks, especially with temperature fluctuations. When warm air inside the tank cools, water vapor can condense on the tank walls and drip into your fuel.
- Faulty Gas Cap: A damaged or missing gas cap can allow moisture to enter your fuel tank. The rubber seal on gas caps deteriorates over time, compromising its ability to keep water out.
- Intentional Contamination: Unfortunately, vandalism where someone deliberately adds water to a gas tank does occur. This is one reason to consider a locking gas cap.
- Improper Fuel Storage: If you store fuel in containers for extended periods, condensation can build up, especially if containers aren’t filled completely or sealed properly.
Avoiding the Problem in Future
Unfortunately, while rare, some gas stations out there 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 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 whether they have a bone to pick with you or simply 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 fuel from the bottom of the tank, which means that the water will be drawn through first. This is why you’ll experience problems quickly.
Should I Drive My Car in This Condition?
It’s another difficult question 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 this 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.
Gasoline vs Diesel Differences
Water affects diesel and gasoline engines differently:
Gasoline Engines
- Gasoline tends to separate from water more quickly
- Less prone to microbial growth but more immediate performance issues
- Water can cause more immediate stalling in gasoline engines
- Often exhibits more obvious symptoms like white smoke and rough running
Diesel Engines
- Diesel fuel naturally attracts and holds more water than gasoline
- Water in diesel promotes microbial growth (“diesel bug”) that clogs filters
- Cold weather can cause water in diesel to freeze, blocking fuel lines
- Modern diesel engines with high-pressure injection systems are more sensitive to water contamination
- Symptoms appear at lower water concentrations than in gasoline engines
Treatment Differences
- Diesel-specific water removers are formulated differently than gasoline additives
- Diesel systems often need biocide treatment in addition to water removal
- Professional diesel fuel system cleaning is typically more expensive
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Thank you.
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?
Fuel filters are designed to filter solid contaminants out of a liquid. It cannot distinguish between water and gasoline in that way.
Retro-fitting a fuel/water separator such as those found in diesel powered vehicles is costly and not as practical as one might think.
THANK YOU
10 reasons on why my car will only run with my froot on the gas and as soon as i take my foot off the gas it dies
Check out this article. A car that starts then dies immediately will have many of the same symptoms as a car that requires you to hold your foot on the gas pedal to keep it running. http://oards.com/causes-of-a-car-starts-then-dies-immediately/
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.