6 Symptoms To Detect Water In Boat Gas Tank & Ways to Deal with It

Whether you are a recreational boater or a professional, it’s essential to know the signs of water in your boat’s gas tank. While water can get into the fuel system in several ways, this issue can create various problems and impact performance and safety.

The common symptoms of water in a boat’s gas tank include engine misfiring, hard starting, stalling, or reduced performance. Other symptoms may include fouling spark plugs and an irregular idle.

As a boat owner, it’s vital to look for any signs of water in the gas tank. Learning the reasons can help maintain your boat and prevent damage, so read on to discover what to look out for.

How Do You Know If You Have Water In Your Boat Gas Tank?

Here, we will discuss the water in boat gas tank symptoms and how to tell if your boat gas tank is contaminated.

Symptom 1: Trouble Starting

One of the most precise indications of water in the gas tank is difficulty starting the engine. Water does not compress the same way gasoline does, so the motor will struggle to start with a tank of watery fuel. 

If you crank the starter longer than usual and do not hear the sound of the engine running, water in the tank may be a culprit.

Symptom 2: Erratic or Sputtering Performance

One of the key signs of water in the gas tank is erratic or sputtering performance while your boat is running. Water may be the reason if you notice speed fluctuations or your engine stuttering. 

Usually, this is because the water isn’t ignitable, so that the fuel won’t combust. Ultimately, this can result in the engine stalling, seizing, or even hydro lock to the cylinders.

Symptom 3: Black Smoke Out the Exhaust

If you’re seeing black smoke from your exhaust while your boat is running, this is also an indication that your fuel is contaminated with water. 

The smoke is an indication that the contaminated fuel is burning incompletely. This is due to the mixture of water being non-combustible, so it won’t completely burn off with the fuel.

Symptom 4: Discolored Fuel

Another way to tell if water is in your boat’s gas tank is to check the color of your fuel. If your fuel has a cloudy, murky color, then this may point to water contamination. 

Also, checking for the presence of water bubbles can often give you an idea of how severe the contamination is and how much is present in the tank.

Symptom 5: Corrosion of Metal Components

If too much water is in the fuel, corrosion may occur. This can be seen on metal components throughout your fuel system, such as the hoses, fuel injectors, fuel pumps, and engine block. 

Rust-deduced areas may be a sign that the water has already caused corrosion.

Symptom 6: Fouled Spark Plugs

If the boat’s gas tank has water, this can also affect the spark plugs, causing them to become fouled. Spark plugs are responsible for igniting the air-fuel mixture inside the engine. 

So when they become fouled due to water in the fuel, the engine will fail to run correctly. This is because the fouled spark plugs can’t generate sparks, resulting in misfires.

10 Possible Reasons Water Gets into Boat Gas Tanks

Knowing what symptoms to look out for and the potential reasons for water in the gas tank will help you prepare your boat for summer fun. Here are possible reasons for water in your boat gas tank: 

  1. Poor Fuel Tank Ventilation 
  2. Worn Out Tank Gaskets 
  3. Damaged Fuel Lines and Filters 
  4. Low Water and Fuel Separator 
  5. Corroded Fuel Tank. 
  6. The gas cap is broken
  7. Condensation in the fuel tank
  8. Fuel tank filler necks leaking
  9. High ethanol Pb content
  10. Old fuel for a long time

How Much Do You Have To Spend To Get Water Out Of Your Boat Gas Tank?

It’s best to get started on draining the water from your boat’s gas tank as soon as possible. Water in the tank can cause severe damage to the entire fuel system, from the fuel lines to the engine itself. 

So, how much do you need to spend to get water out of your boat’s gas tank? Let’s look at the costs of removing water from a gas tank.

Gas Line Flush$50 to $200$50-$300
Fuel Pump Replacement$500 to $1000$250=$500
Fuel Tank Drain and Flush $50 to $300$50-$300
Fuel Injectors Replacement$300 to $600$150-$200
Fuel Filter Replacement$50 to $100$50-$100
Engine Overhauling $2000-$5000~

Tips For Maintaining The Boat Gas Tank To Prevent Future Water Issues

By following these tips, you can minimize the chance of water entering the gas tank and minimize unnecessary repairs and maintenance. 

  • Add a fuel stabilizer if the boat sits idle for an extended period
  • Before a boating season, inspect your boat’s fuel items
  • Make sure the fuel tank vent is clear and the seal works correctly 
  • If running with ethanol fuel, add a corrosion inhibitor to protect the fuel, lines, and other components
  • Replace the fuel tank and fuel lines once every five years if they show signs of wear, tear, or corrosion
  • always store fuel in containers at least 10 gallons in size and never transfer more than five gallons at once
  • Never overfill the tank, and correctly seal and secure the cap when filling up


Here are a few frequently asked questions to help you understand water contamination symptoms and tips on how to avoid it.

How can I remove water from my boat’s tank?

Draining the entire tank and then refilling it with fresh fuel is the best way to remove the water from your boat’s tank. You can also use a wet vacuum or squeegee to remove the water manually. 

Is there a way to identify that water is present in the fuel?

Fortunately, there is a quick and easy way to test for water in the fuel. By opening the fuel line near the water separator and allowing the fuel to run into a clear container, water droplets will be evident.

Is it safe to drive with water in my boat’s gas tank?

No, boating with water in the gas tank is unsafe. The increased moisture can significantly reduce the efficiency and performance of the engine and can even cause it to seize. 

Can ethanol fuel attract water into the gas tank?

Yes, ethanol fuel E10 and E15 can attract water into the gas tank when the fuel is exposed to moisture for an extended period due to phase separation.

How long does an average boat engine last?

The typical lifespan of a marine gasoline engine is 1,500 hours before a complete rebuild is required. Marine diesel engines typically last three times as 5,000 hours under similar operating conditions.


Water in a boat gas tank has severe consequences, reduces performance, leads to corrosion, and even causes engine failure. Regular maintenance of a boat gas tank is essential to ensure optimal performance and a safe ride. 

Taking the time to check that the proper fuel is used, the vent is open, and the tank is secure and tight can help prevent water from getting in. Cleaning the tank and fuel lines can also help keep water out. 

Lastly, a good quality fuel filter can help stop water from getting into the fuel and prevent other deposits from clogging up the system. Taking the time to regularly maintain a boat gas tank can save time, money, and hassle.

Similar Posts