5 Symptoms of Bad Gas in the Boat and Ways to Deal with It

Are you having trouble starting your boat after a long gap? There’s a good chance your boat contains bad gas. It’s a normal thing to happen if you leave your boat unused for a long time. However, how do you know it’s bad gas? You need to look for the signs.

The most typical signs of bad gas in a boat include foul smells, color changes in the gas, and stalling. While the majority of these symptoms have other causes as well, bad gas is one of the strong reasons these symptoms appear.

To properly deal with the issue, you would need to be knowledgeable about the subject. Continue reading to learn more about the signs and a quick guide to safely getting rid of the bad gas.

How To Tell If You Have Bad Gas In Your Boat?

Poor maintenance is often behind the safety issues regarding any vehicle. This can also cause your boat’s gas to go bad. 

Before you take any step, it is essential to confirm that the gas is bad. The following symptoms may help you determine if your boat has bad gas. 

Symptom 1: Change in Smell

The first thing you will notice when your boat’s gas turns bad is a change in smell. 

If you leave the same gasoline in your boat for a long time, it can get old and change its smell. You would get a pungent varnish-like smell which is not so pleasant. 

Symptom 2: Change in Color

Another big symptom will be the change in color. Usually, the best-grade gasoline should have a transparent color. If you find the gas in your boat a bit darker, the gas has gone bad. 

It happens because of oxidation. The transparent color starts to change and slowly turns a bit yellowish. If you notice a color change in the gas, you may need to replace it. 

Symptom 3: Water in the Fuel Tank

If you notice a separate layer of water and gasoline inside the fuel tank, the gas is no longer good for your engine. 

This happens when you leave your boat unattended for a long time, and the tank is not full. 

Also, bad gas often releases moisture and separates from water content. You may find a layer of water and a thick, gummy substance. 

This is known as phase separation. Water in fuel can cause stress to the engine and lead to clogging. 

Symptom 4: Engine Sputtering or Stalling

Any foreign element or dirt in the fuel can interfere with the fuel system, causing the engine to sputter or stall while running. 

If you suddenly start facing this issue when you start or try to run the boat, it can be bad fuel behind it. 

However, when you start noticing the issue, you should check if the fuel filter, fuel tank, and injectors are working fine.

Symptom 5: Requiring More Fuel Than Normal

If you realize that your boat requires more gas than necessary, it may be because of bad gas. Bad gas means the gas is losing its combustibility. 

Although you will need more fuel, you won’t be able to go as far. The engine will struggle to accelerate. 

What Happens If You Get Bad Gas In Your Boat?

Bad Gas in your boat is one of the main reasons for a troubled engine. It is a common issue. Following are some basic issues you may face due to bad gas in the boat. 

  • The engine may start malfunctioning 
  • Severe, irreparable damage to the engine
  • Decreasing fuel economy
  • Low engine efficiency 
  • Decrease in acceleration power 

How Do You Get Bad Gas Out Of A Boat?

If you have bad gas and face issues due to this, you will have to get it out of the system. Following is a simple step-by-step guide to getting bad gas out of a boat. 

Step 1: Drain bad gas from the tank

Drain bad gas out of the tank using a suction pump. Make sure that you empty the tank. Keep the drained gas in a secured container.

Step 2: Clean the fuel tank properly

You need to clean the tank properly to clear any contaminants and debris. You can use a suitable cleaner to remove all the dirt. It will also safeguard against future pollution. Then you need to rinse the tank with water. 

Step 3: Drain dirty water from the tank

Now you need to remove all the dirty water from the tank. Collect the water in a separate container. This should clean the tank. Now you can fill it up again with clean and fresh gas. 

Step 4: Contact your local recycling facility beforehand to discard the bad gas

It is an important step. You can’t discard bad gas taken out of your boat just anywhere. Contact your local recycling facility beforehand to ensure that the bad or degraded gas is disposed of properly.

Tips For Preventing the Formation Of Bad Gas in Boat At The First Place

Bad gas is extremely harmful to the engine. The symptoms may not be easily visible at first. 

However, when they do, they are already pretty bad. Taking some necessary steps beforehand is better to protect your boat from damage. 

  • Avoid steering on nasty water
  • Avoid opposing currents 
  • Don’t load your boat with unnecessary stuff
  • Change the oil regularly
  • Keep the air filter clean and replace it if necessary 
  • Replace the spark plugs regularly 
  • Try to rest your boat in a dry place
  • Use proper fuel additives or treatments


Bad gas in a boat can be dangerous if not dealt with correctly. Now that you know the symptoms of bad gas in the boat, let’s check some frequently asked questions.

Ethanol gas or ethanol-free gas – which is better for a boat?

When it comes to mileage, ethanol-free gas is better. Also, it is better for the engine of the vehicle. It is recommended to use gas with no more than 10% alcohol content. Too much Ethanol can lead to rusting of engine parts. 

How long is it safe to use old gas in a boat?

It is considered safe to use old gas within 3 months. If the gas is free of alcohol, it should be safe within 6 months. However, experts suggest 50 days as a safe storage time for gas, so it’s better to use up all the gas within that time. 

Is it safe to leave gas in the boat?

According to experts, leaving gas in the boat unattended for a long time is not safe. During winter, ice can form and clog the pipeline. On the contrary, a temperature increase can heat the gas during summer, leading to extreme danger.

What is the best way to detect bad gas in a boat?

The best way to tell if the gas has gone bad is by the smell. It should be fine and safe if your gas smells fresh and new. If it smells stale or sour, it’s a sign that the gas is going bad.

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