8 Water in Gas Tank Symptoms (How To Check & Fix)

Every vehicle owner can agree that dealing with water in the gas tank is troublesome. Not that anyone would intentionally do it, but it can happen due to controllable and uncontrollable reasons.

What happens if you put water in the gas tank? Problems from fuel contamination can lead to severe lubrication and engine dysfunctions and compromise one’s safety on the road. Knowing how to diagnose and resolve these problems is a must.

Understanding telltale signs is the first step. Symptoms of water in the gas tank include misfires, rough acceleration, and hard-starting conditions, to name a few. While most can be fixed by a fuel line flush or using additives, others may require replacing your fuel tank entirely.

Determining early signs of fuel contamination and fixes will not only help you avoid unforeseen repair costs but also ensure your car is safe to drive anywhere. That said, below are 8 of the most common water in the gas tank symptoms:

  1. Sputtering
  2. Power surges
  3. Engine hesitation
  4. Starting difficulties
  5. Phase separation
  6. Corrosion
  7. Strong gasoline smell while driving
  8. Misfiring or rough idling

Some of these signs are not exclusive to water-in-tank issues and would need to be narrowed down accordingly. Others may be too obvious and tempting to overlook. However, do not be fooled by the seeming simplicity of these symptoms, as they can lead to engine seizures if not resolved immediately.

Car Fuel Tank Open Lid

8 Water in Gas Tank Symptoms

1. Sputtering

Although deliberately putting water in the gas tank is highly unlikely for any driver, it does accidentally happen at times. And as a result, the engine behaves erratically.

The reason for this is that water is non-combustible. Hence, it tricks MAF (Mass Air Flow) sensors and the like to think that fuel (and not water) is entering the combustion chamber.

This trickery messes with the air-fuel mixture, causing the engine to run lean and exhibit giveaway signs such as sputtering, volatile changes in speed, or poor performance.

2. Power Surges

An abrupt increase or decrease in power happens if water gets in your gas tank. You may notice intermittent power loss or out-of-the-blue surges when driving. A vehicle would act up since it is not intrinsically designed to compress water during acceleration, resulting in the engine noticeably losing power.

Inversely, power sky-rockets as soon as cleaner petrol or diesel is injected through the fuel system into the engine. A water-contaminated fuel tank would most likely be the culprit, provided there are no accompanying sensor problems or engine faults. Otherwise, power surges could point to other issues.

3. Engine Hesitation

If you experience power or mileage issues or suddenly have trouble getting up to freeway speed limits despite nothing wrong with your vehicle, start looking into possible water in the gas tank.

This vehicle behavior is more of an outcome than a symptom. With lots of water in the gas tank, a car would show hesitation when pressing on the accelerator pedal and even be accompanied by jerking or sudden speed fluctuations. The bottom line is it makes your daily commuter unsafe to drive.

4. Starting Difficulties

Worst-case scenario, an engine will refuse to start if a pool of water is on top of the piston as you crank the motor. Because water is incompatible with the fuel system, it dampens the combustion needed to rotate the pistons and start a vehicle. If any water is in the tank, you will be able to start a car but with great difficulty at best. But if the water volume is high, expect a no-start issue.

5. Phase Separation

Because water is denser than fuel, the latter will naturally float on top of the former and cause water to sit at the bottom of the fuel tank. When this happens, the phenomenon is called phase or water separation.

Several things can cause it:

  • Condensation due to sudden temperature change or inclement weather
  • Broken or loose gas cap
  • Fuel sitting idle for extended periods (causing its components to split, especially for ethanol-containing fuel variants)

Any of these factors is unintentional and can pretty much be avoided.

6. Corrosion

A rusty gas tank or fuel pump results from phase separation or water settling at the bottom once inside the fuel tank. The challenge here is that most of the actual damage occurs or becomes apparent when the gas/diesel reservoir is close to empty. Consequently, the pump starts to pull in water from the bottom, leading to rust formation around the fuel tank and eventually damaging connected fuel system components or the tank itself.

Fuel tanks are each made differently – plastic polypropylene, high-density polyethylene, plastic adhesive, regrind plastic, iron, steel, or aluminum – and, based on its composition, will have different resistance levels or immunity to rust formation. For instance, a steel gas tank would have a higher proclivity to rusting if water is absorbed in it.

In this scenario, removing the entire fuel tank is necessary to determine the amount of rust present inside. However, replacing the fuel tank altogether may not always be the solution to preventing further fuel contamination.

7. Strong Gasoline Smell While Driving

Naturally, vehicle owners assume a strong gasoline smell to mean unburned fuel vapors from the tailpipe or a simple fuel leak – both of which would warrant either patching up cracks or holes caused by wear or performing engine tuning that is long overdue.

But seldom does it occur to most of them that the situation calls for a full-on repair of the fuel tank. After all, the damage can be due to phase-separation-driven corrosion slowly eating away at fuel components.

So, the next time you encounter leaking injectors or fuel dripping on the engine exterior, make sure to thoroughly inspect the fuel tank itself and do repairs or replace parts as needed.

8. Misfiring or Rough Idling

This indicator appears often and is associated with several vehicle issues (not just with water in gas tank symptoms) – and here is why. Most vehicles produced in the past two decades come with an injector instead of a carburetor. These fuel injectors have pores designed to spray the required amounts of fuel (with the appropriate density), facilitating its flow into the combustion chamber. If water is in the gas tank and mixes with fuel, this upsets the density of fluids fuel injectors can handle, putting stress on the latter and eventually causing the engine to fizzle out.

How Much Water Will Ruin a Car?

Hand Opening Car Fuel Tank

A small amount in the gas tank is normal. After all, all forms of petroleum (including fuel) have a small amount of dissolved water in their composition. E-10 fuels, for instance, usually have up to 0.5% by volume. When water volume is this small, it will not be enough to cause trouble or even give noticeable indications.

The real problem starts with considerable amounts of free water mixing in with the fuel in your tank. By quantity, many vehicle owners say a full cup of water at most is pretty manageable and will not necessarily hurt a vehicle’s engine. Fuel additives are still effective when working with this much. But any more than a full cup of water will most likely lead to serious car problems.

Sources of Fuel Contamination

Aside from the usual water in the gas tank symptoms enumerated in this guide, the following situations are some examples of how water gets mixed in with our fuel without our knowing:

  • Your favorite pump station might have faulty gas pumps or intentionally sell watered-down fuel.
  • A gas station crew (or you) may have forgotten to tightly replace the gas cap after refueling, allowing water to get inside.
  • You may not be aware you have a broken or worn gas cap.
  • Condensation caused by temperature changes can accumulate water vapor that easily gets inside a loosely sealed tank.
  • The fuel pump or other fuel system component might be damaged, resulting in fuel contamination.
  • Groundwater might have seeped into the pump station’s storage tank, diluting fuel unintentionally.

Prevent Water From Getting into your Gas Tank

To prevent these situations from causing water to get inside your fuel tank, you will need to take certain precautions. Be careful in choosing where you fill up your fuel tank and veer away from old pump stations or flood-prone areas as much as possible. Ensure not to remove your gas cap when you do not need to, especially before going to a pressurized car wash. And always examine the state of your top fuel pump and replace worn-out parts as needed.

Actively checking the presence of water in your fuel tank even before symptoms show is another thing you can do. Examine the color and smell of your fuel from time to time. You may also lace your dipstick with a water-finding paste to help detect if your fuel is water-contaminated. Also, verify there is no microbial growth or algae in your tank and that fuel is not too dark-colored.

Other Recommendations

Other helpful recommendations to keep water-in-gas-tank issues at bay are as follows:

  • Check for water every month. You may need to do this more frequently if you have experienced heavy rainfall recently in where you live.
  • When loosening your gas cap, always listen for a slight hissing sound (the sound of depressurizing the fuel tank). If there is none, it is time to upgrade to a locking fuel cap.
  • Decide on a water depth limit before taking remedial actions (This limit will largely depend on the shape and size of your tank, but some car owners suggest going with a threshold of 2.0 inches for diesel and 0.25-0.50 inches for the rest of the fuel variants.
  • Never let the gas in your tank go idle for a month or more.
  • Have a contingency plan for remediating phase/water separation. This item should not be a concern if your tank has drain valves at the bottom.

Vehicle savants swear by adding ethanol to their fuel tank. However, I chose not to include it in the above list since ethanol is erosive in nature and may result in more harm than good to your gas tank and entire fuel system.

How to Fix Water in the Gas Tank (7 Tips)

In some cases, we could miss catching the presence of water early on and find ourselves with car troubles. Luckily, there are methods we can employ before consulting a professional mechanic. Here is a non-exhaustive list of some of those effective remedies:

  1. Fill up the tank with high-quality fuel, which works wonders in mild fuel contamination cases. The water gets saturated in the premium gasoline and eventually burned off by the motor.
  2. Eliminate small amounts of water by pouring fuel additives into a tank full of gasoline. You can choose between emulsifying-type and demulsifying-type options.
  3. In situations where there is more water in the tank than gas, immediate displacement is the best method. Siphon out the old gas while immediately placing a high-octane variant in the tank.
  4. For large volumes of water in the tank, drain the gas tank and let it dry before refilling it with premium, non-contaminated fuel.
  5. Add rubbing alcohol to contaminated fuel, which helps absorb the water and settle at the bottom of the gas tank. Since rubbing alcohol is combustible, it will pass through to the engine without turning into extra residue.
  6. Pouring a large amount of octane booster into the water-contaminated fuel will help get rid of water content.
  7. Flushing the fuel lines or draining them for thorough cleaning minimizes rust formation and prevents leaks from occurring.

You should be able to perform these remedies without fail if you are well-versed with vehicles and their systems. But if you feel uncomfortable or skeptical, speak to a trusted mechanic and ask for help.

Conclusion – Water in Gas Tank Symptoms

Car Fuel Tank and Rain Water

To recap, here are 8 water in the gas tank symptoms you should look out for:

  1. Sputtering
  2. Power surges
  3. Engine hesitation
  4. Starting difficulties
  5. Phase separation
  6. Corrosion
  7. Strong gasoline smell while driving
  8. Misfiring or rough idling

It is essential to address this problem with urgency. Repair costs are not necessarily high if only replacing filters and fuel system components (plus labor). But if this issue is left unresolved for a long time, this amount can quickly escalate. Ultimately, nothing beats diligence in the upkeep of your vehicle and having it serviced by an expert mechanic.

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