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.

[scottar]

Do you have a fuel gauge sender - leaking perhaps? The two vents coming in at the back to me would indicate the tank could very easily trap an air pocket in the front. You could try storing bow down once the bilges are dry. Possibly also look at better hose clamps. Is the smell stronger in the cockpit of the boat or outside of the boat. Fuel vapour is heavier than air so it tends to sink. I quite often leave tote tanks in an under floor storage area on my rig that is certainly not air tight but when I pop the floor panel I will be able to smell fuel - even though there was nothing evident standing in the boat. Might give some indication as to whether the leak is internally in the boat or definitely coming from the breather.

[darren11]

Sounds like I need to lift the floor and check hose clamps etc. occasionally I have noticed a fuel smell when opening the storage hatch under the bunks in the cabin.
Needs further investigation.
Thanks

[shakey55]

Sounds to me like a small leak from somewhere. You need to investigate.

Pull those breather hoses off. A mate pulled his of several years ago as having a similar problem. Both hoses clogged up with small spiders and bugs in their webs.


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[darren11]

Thanks shakey55 will look at lifting the floor above the tank and check it all over.

[Dignity]

Mine turned out to be the sender unit, leaking through the central bolt hole. There is a seal and a large ribbed plastic washer on top but the 5/16" nut and small washer eventually bowed it inwards after tightening it, I replaced the small washer with a large diameter one similar in size to the plastic one and replaced the seal, doesn't leak there anymore. I replaced the hose between the tank and filler tube but it was oversize and now it leaks from there, I cant seem to find a supplier of 2" fuel proof hose, the last one I got from Pirtek as I said is larger and near impossible to clamp down tight due to the armour wires in it.

If you can get your tank out you can pressure test it but still may not show where it's coming from. I sprayed detergent all over including the sender unit and no leaks eveident, fuel vapopur seems to need the tiniest hole or crack to be smelt. When you do get your floor up you might find spots of purple on your tank, these are where the fuel vapour has condensed and in 99% of cases has no bearing on where the leak is if it is relatively small.

[stevej]

B & B industrial carry fuel proof 50-60mm fuel hose and has no wire internals
i had to get some for the filler neck on my mid 60s ford

[ozynorts]

I cant seem to find a supplier of 2" fuel proof hose, the last one I got from Pirtek as I said is larger and near impossible to clamp down tight due to the armour wires in it.



Is this the size your looking for mate?
https://www.santmarine.com.au/index.php?option=com_jcart&Itemid=209&route=product/product&path=34&product_id=116

[inveratta]

I have had similar sort of issues with a replacement tank,breather at the aft end top of tank...on a hot day in the drive it can burp out an "alarming" amount of fuel....I did a couple of simple things to confirm it was pressure related....cracked the filler cap, bow end of tank.and felt the pressure release.... and wound the trailer wheel at the coupling end so the bow was down and the stern up.....Made me think that you probably need a vent at both end of the tanks to cover both situations.I cant think that the stabilizer has anything to do with it...

[stevej]

stabliser also has to go in when the fuel is fresh

expensive exercise adding in weeks later for nothing

[Noelm]

Is this the size your looking for mate?
https://www.santmarine.com.au/index.php?option=com_jcart&Itemid=209&route=product/product&path=34&product_id=116
I got my fuel filler hose from Clarke Rubber, they had a few different sizes and reasonably cheap.

[Dignity]

Noel. Clark rubber here don't carry anything that Size here,35mm I think is the biggest.

Ozynorts. Buying a meter without being able to put the vernier across is a hit and miss, I measured a 50 mm pipe (not fuel resistant) today and it measured 54 mm ID.

Steve, I'll have a look at them. I also got a suggestion of another mobile supplier on the Sunshine Coast so I'll give them a go.

[Dirtyfuzz]

Noel. Clark rubber here don't carry anything that Size here,35mm I think is the biggest.

Ozynorts. Buying a meter without being able to put the vernier across is a hit and miss, I measured a 50 mm pipe (not fuel resistant) today and it measured 54 mm ID.

Steve, I'll have a look at them. I also got a suggestion of another mobile supplier on the Sunshine Coast so I'll give them a go.

Fishing international on Parkyn parade stock it mate, just replaced mine recently


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[scottar]

Noel. Clark rubber here don't carry anything that Size here,35mm I think is the biggest.

Ozynorts. Buying a meter without being able to put the vernier across is a hit and miss, I measured a 50 mm pipe (not fuel resistant) today and it measured 54 mm ID.

Steve, I'll have a look at them. I also got a suggestion of another mobile supplier on the Sunshine Coast so I'll give them a go.

If you get stuck with the local's Sam, Try these guys. Great service at the Hemmant branch. We get a lot of gear for work through them.

https://www.hosesuppliers.com.au/contact-us

[Dignity]

Darren,sorry to hijack your thread,it was unintentional. Hope you find your leak as they are a PIA and also a hazard.what sort of boat is the tank in and where are you located.