Boat Fuel Tank Vent Open or Close (What to do?)

Vents for boat fuel tanks may seem small and distracting but it has a great role in motor functioning. Though, some boat owners are confused and having trouble on whether the boat fuel tank vent is open or closed.

The opening and closing of vents vary in the situation you’re in. Look at the other scenarios explained below to understand the ventilation process of a boat fuel tank. 

boat fuel tank vent open or closed

Boat Fuel Tank Vent: Open or Close

Vents act like lungs, it is responsible for the entry and exit of air in the boat fuel tank.

Just like filling fuel into the tank, it is impossible with pressurized air in it. The same goes in withdrawing fuel, air must enter first before you extract it successfully.

Now the awaited question about boat fuel vents will be answered underneath.

When to open a boat fuel tank vent?

In sailing a boat, the gas tank should pump the fuel towards the motor to make it work.

When the vents are not open, this vacuum blockage occurs where the pressure inside the tank obstructs the passage of fuel to the motor.

Opening the ventilation before running the boat is the solution.

Through this, the vacuum and pressure stuck inside the fuel tank are released, hence allowing the tank to breathe and carry enough fuel.

Fortunately, modern boats are already featured with exhaust fans that turn on to vent out fuel fumes before starting the engine.

Aside from that, boats, cars, and other items that require fuel have their container. Like plastic tanks, they are manufactured for expansion and contraction.

Some containers tend to shrink, and once the vents are opened, it equalizes pressure inside making the tank expand back to its form.

For everyone’s safety, do not open a fuel tank vent unless you are in an open area with fine air circulation, away from any risk for ignition, and even mobile devices.

When to close a boat fuel tank vent?

Gasoline is made from volatile components, which evaporate quickly especially in a hot climate. That is why proper storage of the fuel tank is essential.

After mooring your boat, ensure to shut the engine, and close the vents from the fuel source. This helps avoid fuel loss. Also preserving it in future fishing trips.

Additionally, unused, and open fuel tanks in the compartment are susceptible to fire due to the release of fumes.

When the evaporated gas meets oxygen, heat, or any source of ignition, expect an explosion to happen.

How to operate venting gas tanks with outboard motors?

Outboard motors are equipped with ventilation in their gas tanks. Some are automatically opened when they detect pressure from the fuel tank. Other outboards have manually operated ventilation.

These vents help overcome the sucked pressure from the fuel pump to the motor. Now, to use a venting gas tank with outboard motors, kindly follow the guide below.

Step 1. Position yourself near the tank before filling it. Focus on listening while you loosen the gas cap. When you hear the air rushing towards the tank, this implies a ventilation problem.

Step 2. For manual vent valves, remove the cap by hand. Fill the tank and secure it by closing.

Step 3. Connect the fuel hose with the tank to the motor. Do not forget to open the vent after to avoid a vacuum block.

Step 4. If your motor starts to “gasp” as you’re getting into your boat, remove the filler cap from the fuel tank. Replace the tank venting system if the motor appears to be starved for gasoline even when the cap is taken off.

Why does my boat fuel tank overflow?

Have you ever tried filling your boat’s tank for a short period but it is already overflowing? Well, there are certain reasons behind this mystery.

Before jumping to a conclusion of having a severely damaged fuel tank, try to consider these common issues reported such as the build-up of clogs, faulty ventilation system, or barrier in the fuel hose.

Clogged Fuel Tank Vent

Over time, seeing your ventilation ports dispositioned, eroded, and already worn out is no surprise especially when it is not maintained.

By looking at the exterior surface of the boat’s fuel tank vent, you can easily assess that there’s a problem. Begin with the filler cap, once it’s removed, blow some air from the outside into the vent.

Remember that some vents are showcased with the screen as filters where dirt gathers. Unscrew the screen then cleanse it thoroughly.

If air comes out of the filler hole, then there should be no issues. But if the air does not pass through the vent, then you should suspect that there’s another problem.

Blocked Hose

If the port is still blocked, check out the vent hose. Usually, owners do not notice the position of the hose.

Sometimes, it is kinked or twisted upwards which allows entry of water into the tank that results in overflowing, so the hose should be facing downwards.

Test the hose again by blowing some air like what you did to the vent.

If the air is still unnoticeable, your last option would be to replace the ventilating port and hose, so you can start filling again without overflowing.

Unfit Venting System

If none of the recommendations worked, maybe your venting system is not a match with the boat’s fuel tank.

Although most vents are built within the boat’s tank, it is unusual to have some fitting issues. However, clogs and dirty fitting can create an issue.

In addressing this, locate the vent fittings on your fuel tank. Remove the vent hose and blow it again to see if there is air.

If none, align the hose because it might be kinked. Also, grab a flashlight and see if there is clogged debris inside it. After cleansing and organizing the connections, repeat inspection.

Extra Maintenance Tips

1. Free the Vent Line

In the standard design, a vent line should cross sideways to the top of the tank until it reaches the hull side, extending up to the vent port. At this point forwards, the hose should be precisely straight, so through gravity, the fuel can return to the tank.

When you are new to handling a boat’s fuel tank ventilation system, ensure that the vent line is free from distractions or simply traps to promote proper air circulation.

2. Clean the Screen

Most boat fuel tank vents are created with screens. They work as flame arrestors and block fuel vapors. However, it gets clogged at some point.

It’s normal for screens to gather unwanted fragments like salt crystals, dirt, and rust if not maintained. This is one of the problems why your gas tank is beginning to get faulty at times.

Cleanse the screen at least once a month or how frequently it clogs. If rust has dominated the vent’s surface, you’ll need replacement.

3. Keep Hulls Dry

The hull’s vertically angled structure is meant to vent fumes away from the boat. Being splashed with water is inevitable, but to minimize impact, attach the hulls higher.

Additionally, markets have been modernizing many vents which offer designs that help drain water. A 90-degree upward model that secures the hoses’ fitting, thus draining the water out.

4. Use a Fuel Surge Protector

A fuel surge protector is an eco-friendly device that is used to avoid the spillage of fuel vents when filling their tanks. Also, it guards the hull against gas stains.

Attwood is one of the many recommended brands that are durable and reliable for they offer a no-spill valve. Moreover, the Green Marine brand is also famous for its audible warning or whistle which indicates the level of the fuel tank.


And there you have it! We hope this short discussion reduces your struggles in deciding whether the boat fuel tank vent should be open or closed. Further inquiries and assistance can be solved by calling an expert.

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