Closing fuel tank vent when not in use?

[darren11]

Should I fit valves and close off the vents when not in use?
I have a 220L aluminium tank in my alloy boat. It has 2 vents mounted on the transom. My shed smells of fuel all the time. Also wondering if this may help reduce fuel loss from evaporation.
I keep the tank full with fuel stabiliser added to keep it fresh.

[scottar]

Something going on there Darren. No issues in my shed at all with fuel smell. I don't top up unless I am fishing the next day and have never used fuel stabilizers either. Is there a chance the breather is having fuel pushed out it due to boat angle?

[scottar]

Just to add - I certainly would not seal off the tank. Chances are it will buckle at best or rupture at worst.

[darren11]

Being that the tank would be at least 3mm alloy. Couldn’t see how it would be any worse than having a 200L drum or mower container that isn’t vented.

[darren11]

Shouldn’t be anything coming out of the breather as it is mounted well above the tank and the Boat is pretty much level.

[catshark]

agree, must be topping up to the max and expansion of fuel is rising up the breather...dont seal it off, its needs to breathe. would this fuel additive change and expand as well due to atmospheric pressures, as ived never used the stuff in my life.

[scottar]

How many breathers in the tank and does it exit forward or aft ?

[darren11]

2 breathers. Mounted side by side. Vents face down mounted facing aft on the transom. 1/2 inch hose.

[scottar]

Meant where it exits the tank but if you have two chances are one fore and aft . Check them both to make sure there are no blockages. It is surprising how much an air pocket can expand on a hot day. If the breathers end up below fuel level and there is still an air pocket above them, it will expand and push fuel out very easily. You could look at fitting an expansion chamber if you do end up figuring out fuel is coming out the breathers. Like I posted - I wouldn't block it - but it's your tank.

[darren11]

Sorry missed that. They are both fitted aft on the tank. I assume either side of an internal baffle.

[DATCOL]

With the tank full the heat expands the fuel & pushes the fumes out the breathers & makes a petrol smell If you get it full enough it will push out fuel

[scottar]

Exiting from the top of ghe tank or the aft end - and if from the end, how far down?

[stevej]

if i filled my 150 liter tank full up to the fill port it would push fuel out the breathers , its a open system it just happens
so i just didnt fill it full

breathers should have a loop in the system

also fuel cans drums are designed to hold some pressure with ribs or pressings on the containers
i doubt boat manufacturers put that much thought into their tanks

[darren11]

From top of the tank

[darren11]

Should of mentioned have noticed this issue with the tank partially filled and before I started using any stabiliser.