How to Remove Water from Gasoline

Water in gasoline is a common problem that can lead to serious issues with your car’s performance and potentially costly repairs. Water gets into gas tanks through various ways like condensation, a loose gas cap, or bad gas station pumps. When water mixes with gasoline, it can cause corrosion in metal fuel system components, damage rubber hoses and seals, and impede engine performance. Removing water from gas tanks quickly is crucial to avoid deterioration of fuel system components.

This comprehensive guide will cover everything you need to know about water in gasoline, including:

  • How water gets into gas tanks
  • The symptoms of water in gasoline
  • The risks and potential damage of water in gas
  • How to test for water in gasoline
  • Step-by-step instructions for removing water from gas tanks
  • Tips for preventing water in gasoline

Follow along to learn how to thoroughly remove water from your gas tank and keep your car running smoothly.

How Does Water Get Into Gas Tanks?

Before learning how to remove water from gas, it’s important to understand the common ways it gets into fuel tanks in the first place. Here are some of the main causes of water in gas tanks:

  • Condensation – Temperature fluctuations cause water vapor to condense and collect in empty spaces in gas tanks. This often happens as temperatures change between night and day.
  • Loose or missing gas cap – An improperly sealed or loose gas cap allows water to seep into the gas tank when it rains or from car washes.
  • Phase separation – Ethanol in gasoline can absorb water and separate from the fuel over time, sinking to the bottom of the tank.
  • Bad gas station pumps – Faulty pumps and underground storage tanks allow groundwater seepage into gas at the station.
  • Flooded engines – If an engine floods or stalls in deep water, water can enter directly through the fuel intake.

How Water Gets into Gas Tanks

CondensationTemperature changes cause water vapor to condense in gas tanks
Loose/Missing Gas CapAllows water to enter through openings in rainy weather
Phase SeparationEthanol absorbs water then separates from fuel over time
Bad Gas Station PumpsFaulty pumps/tanks allow groundwater to mix with gas
Flooded EnginesWater can directly enter through fuel intake in floods

Symptoms of Water in Gasoline

Detecting the signs of water contamination early is key to avoiding significant engine damage. Here are the most common symptoms of water in gas:

  • Difficult starting or engine stalling
  • Rough idle, sputtering, or misfiring
  • Loss of power and acceleration
  • Increased corrosion of metal fuel system parts
  • Check engine light coming on
  • Gasoline appearing cloudy or milky

If you notice any of these issues with your car, especially after refueling during or after wet weather, it likely indicates water in the gas tank. The sooner it is addressed, the less risk of permanent damage.

Common Symptoms of Water in Gasoline

  • Hard starting/engine stalling
  • Rough idle, sputtering, misfiring
  • Loss of power and acceleration
  • Increased corrosion of metal fuel parts
  • Check engine light illuminated
  • Cloudy/milky appearing gasoline

The Risks of Water in Gasoline

Driving with water-contaminated fuel can lead to some very costly repairs if left unchecked. Here are some of the most common damages:

  • Corroded fuel tank and fuel lines – As water causes rust and corrosion of metal components, it can eat through fuel tanks and lines. Replacing them can cost $500 or more.
  • Damaged fuel injectors – Water can cause fuel injector clogs, reduced flow, and failure. Replacing a full set can cost $600-$1000+ for parts and labor.
  • Fuel pump failure – Water exposure can cause fuel pump bearings, brushes, and seals to fail. Fuel pump replacement averages $450-$700 for parts and labor.
  • Clogged fuel filters – Small amounts of water cause filters to clog more quickly requiring more frequent replacement.
  • Engine misfires – Water in the combustion chambers causes misfires, reducing performance and fuel economy.

The repairs above often exceed $1000+ and can leave you stranded if the vehicle becomes undriveable. That’s why addressing water in gas right away is so important.

Potential Damage from Water in Gasoline

DamageDescriptionAverage Repair Cost
Corroded Fuel Tank/LinesRust and corrosion eat through metal tank and lines$500+
Damaged Fuel InjectorsClogs, flow issues, failure$600-$1000+ parts/labor
Fuel Pump FailureBearing, brush and seal failure$450-$700 parts/labor
Clogged Fuel FiltersMore frequent replacement needed$25+ per filter
Engine MisfiresMisfires hurt performance and fuel economy$200+

How to Test for Water in Gasoline

Suspecting you have water in your gas? Here are some methods for testing and confirming:

  • Visual inspection – Drain a sample of gas into a clear container. Water will settle on the bottom with gas on top.
  • Water finding paste – This paste changes color when put into fuel containing water.
  • Water sensor kits – Sensors inserted in tanks detect water and warn with indicator lights.
  • Fuel pressure test – Low pressure indicates restricted flow from water blocking fuel lines.
  • Mechanic diagnosis – Mechanics can detect issues pointing to water in gas during an inspection.

Checking for water regularly, especially after refueling in rainy weather, allows you to address it early before engine damage occurs. If you confirm water presence through testing, you’ll need to remove it promptly.

Methods for Testing for Water in Gasoline

  • Visual inspection – drain sample into clear container, separate water/gas layers confirm
  • Water finding paste – changes color when put into fuel with water
  • Water sensor kits – sensors in tank detect water, light indicators
  • Fuel pressure test – low pressure indicates water restricting fuel flow
  • Mechanic diagnosis – can detect issues indicating water during inspection

Step-by-Step Guide to Removing Water from Gas Tanks

Once you’ve confirmed water is present in your gas tank, here is a step-by-step guide to thoroughly removing it:

Draining the Tank

Draining the entire fuel tank is the most direct way to eliminate all water.

  1. Safely raise and support the vehicle on jack stands if draining from the bottom.
  2. Place an approved gas container below the drain plug.
  3. Locate the drain plug on the bottom of the fuel tank.
  4. Using a wrench, slowly loosen the drain plug 2-3 turns checking for leaks.
  5. Once fuel starts flowing out in a steady stream, open the plug fully to quicken drainage.
  6. Allow the tank to completely drain, then reinstall and tighten the drain plug.
  7. Refill the tank with fresh gasoline to the recommended octane level.
  8. Drive normally to circulate fuel through the engine and lines.

Draining from the top via the fuel filler neck is also an option, though not as thorough. Insert a siphon hose down to the tank bottom and pump out all fuel.

Removing Remaining Water

A full drain may not catch all the water hidden in low areas of tanks. Adding a gasoline drying agent can help:

  1. Purchase a gas-drying fuel additive like isopropyl alcohol or methanol-based Heet.
  2. Pour the recommended amount into a near-empty gas tank.
  3. Fill the tank with fresh gasoline to mix thoroughly.
  4. Drive to circulate the additive through the fuel system.
  5. It will absorb and remove any remaining water.
  6. Change filters after treatment to clear any released deposits.

Repeated treatments may be needed for excessive water. More stubborn cases may need a mechanic to flush the tank.

Step-by-Step Guide to Removing Water from Gas Tanks

  1. Drain the Entire Fuel Tank
    • Safely raise and support vehicle
    • Place approved gas container below drain plug
    • Locate and open drain plug, let fuel drain out
    • Ensure tank fully drains, close and tighten drain plug
    • Refill tank with fresh gasoline
  2. Remove Remaining Water with Drying Agent
    • Purchase gas-drying additive like Heet
    • Pour recommended amount into near-empty tank
    • Fill tank with gasoline to mix
    • Drive to circulate additive, absorbing water
    • Change filters to clear released deposits

Tips for Preventing Water in Gasoline

Prevention is the best medicine when it comes to avoiding water contamination in your gas. Here are some helpful tips:

  • Always re-seal the gas cap tightly after refueling. Listen for it to click.
  • Top off the tank when refueling to minimize air space for condensation.
  • Avoid pumping gas when it’s raining or just finished raining.
  • Fill up more frequently to prevent condensation from temperature swings.
  • Add fuel stabilizer like Sta-Bil to help prevent phase separation.
  • Inspect filler neck seals and replace any cracked or dried out seals.
  • Check fuel cap tightness periodically. Replace if the seal is worn out.
  • Ask station owners to check pumps/tanks if you repeatedly get bad gas from a location.

Remaining diligent with prevention measures will go a long way in keeping water out of your gas tank and saving you from headaches down the road.

Tips for Preventing Water in Gasoline

  • Re-seal gas cap tightly after refueling
  • Top off tank when refueling to minimize air space
  • Avoid pumping gas when raining
  • Fill up more frequently to prevent condensation
  • Use fuel stabilizer to prevent phase separation
  • Inspect/replace worn filler neck seals
  • Check fuel cap tightness periodically
  • Ask owners to check station pumps/tanks for issues


Water finding its way into gas tanks is an annoying and potentially damaging problem for vehicle owners. Identifying symptoms like stalling, corrosion, and power loss quickly and testing for water contamination is key to addressing it promptly. Draining the entire tank and using drying agents gives the best chance to thoroughly remove all water present. But the best defense is preventing water from getting in at all through diligent maintenance and refueling habits.

With the knowledge provided in this guide, you can banish water from your gas tank, avoid costly repairs, and keep your car running smoothly for the long haul. Just remember to act fast at the first signs of trouble and use preventative maintenance steps, and you’ll have smooth sailing ahead.

Key Takeaways:

  • Water can sneak into gas tanks through condensation, loose caps, phase separation, bad pumps, and flooded engines.
  • Symptoms like stalling, corrosion, and power loss indicate water may be present. Testing methods can confirm it.
  • Water can damage fuel system components like tanks, pumps, and injectors costing $1000+ to fix.
  • Draining the whole tank and using drying agents is the best way to remove water. Prevention is ideal.
  • Keep gas caps sealed, top off tanks, use fuel stabilizers, and avoid wet weather refueling to stop water from getting in.

Citations: [1] [2] [3] [4] [5] [6]

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