Why Should A Boat’s Gas Tank Never Be Completely Filled?

Why Should A Boat’s Gas Tank Never Be Completely Filled?

Owning your own boat can be a challenging task as there is a lot of maintenance and care that comes with it.

However, there are lots of things you can do to keep your boat in excellent condition – and one of them is simply never filling your boat’s gas tank to full capacity. But why shouldn’t you completely fill your boat’s gas tank? 

If you are wondering what would happen if you field your boat’s gas tank to full capacity, then this is the place for you.

We are going to be taking a look at what happens when a boat’s gas tank is completely filled – and why you should never do it yourself! 

Why You Should Never Fill Your Boat’s Gas Tank Completely

There are actually two main reasons why you should never fill your boat’s gas tank to full capacity, and these reasons are because a full tank causes dangerous gas vapor leaks and also causes gas to overflow from your tank when your boat is in action. 

Let’s explain each reason in full detail.

A Full Tank Causes Gas Vapor Leaks

The main reason why you should never fill your boat’s gas tank is that a full gas tank can cause dangerous gas vapor leaks.  

In every gas tank, there is a type of gasoline vapor – a dangerous fume created by stagnant gasoline as it sits in its container or tank, waiting to be used.

This gas vapor takes up a chunk of the space in the gas tank and without that space, you are putting your boat in danger of creating a gas vapor leak. 

As you fire up your boat and start burning fuel, the fuel in the fuel tank is going to get warm. As this happens, the gas molecules expand and start to move around more as the heat provides them with more energy.

The air above the gas will grow warmer too and will start to expand. 

This means that when you fire up your boat and your gas begins to heat up and expand, it’s important that there is room left in your boat’s gas tank to allow for this.

If not, then the dangerous vapors created by your gas will be pushed up and out of the fuel tank through the vents. 

Gas vapor leaks are extremely dangerous as they contain particles of gasoline, making them toxic and sometimes flammable if gathered in dense enough quantities. As a result, a gas vapor leak could result in a fine for you!  

So, it’s important not to fill up your gas tank on your boat. If you leave room for the gas vapor, then even when it expands, there’s plenty of room in the gas tank for it to stay there without overflowing and leaking. 

A Full Tank Causes Gas Overflow 

Another reason why you should never fill your gas tank entirely is that a full tank can cause actual liquid gas to overflow. 

Filling up your boat’s tank with fuel means that it’s likely your gas will overflow to other parts of the boat’s engine and fuel system as it sloshes around with movement.

Think of it as trying to carry a bowl full of water – some water is definitely going to spill over the side, no matter how careful you are. The same is true for your full gas tank – some of the fuel is going to spill up and over into other parts of your boat. 

One of the most notorious places for fuel leaks is the fill hose on your boat’s gas tank. 

The fill hose is designed to carry fuel but not to store it, which means that if your gas tank does overflow due to it being too full, then some gasoline is going to get stuck in your fill hose.

Because fill hoses are not designed for prolonged storage of gas, the gas can break down and damage your fill hose. Over time, it could even break through entirely and leak onto other parts of your boat! 

So, filling your boat’s fuel tank with too much gas means that it’s likely that some of that gas will overflow into other parts of the fuel system and cause damage there. 

How High Should You Fill Your Boat’s Gas Tank?

So, by now you know that you should never fill your boat’s gas tank completely – but what is the maximum level you can safely fill your boat’s gas tank? 

It’s recommended that you never fill your boat’s gas tank over 90% of its capacity.

This means that the 10% of space left in the tank is enough for gas vapors to form and expand in without leaking, and it gives the gas itself a little wiggle room to slosh around when the boat is moving.

This 90% also includes any fuel additives you have added to your gas tank. So, ultimately, your boat’s gas tank should always have a minimum of 10% free space to allow vapors to form and grow without causing any overflows or leaks. 

Can You Fill A Boat’s Gas Tank For Storage? 

When storing your boat for the winter (or perhaps you just don’t plan on using her any time soon) then it’s widely recommended that you fill up your boat’s gas tank to 90% capacity. 

Although it may be tempting to store the gas tank as empty as possible to avoid wasting fuel, this actually can damage the engine. 

This is because if you store the gas tank with any less fuel, then you are leaving enough space for air to get into the tank, react with the gasoline, and cause condensation which can corrode your boat’s gas tank.

If you store a fuel tank that is at 90% capacity, then the fumes and vapor will help keep any water out – and stop your fuel tank from corroding. 

In Summary

So, you should never fill your boat’s gas tank any higher than 90%. A full gas tank can cause vapor leaks and gas overflow which can cause some serious damage to you and your boat.

If you are storing your boat for a long period of time, then ensure your boat’s gas tank is at 90% capacity to deter phase separation and corrosion in your gas tank. 

We hope this guide helped you understand your boat’s gas tank a lot more! 

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