Expanding Fuel

[shakey55]

Good afternoon to all.

I have a 2000 model Seafarer V-Sea with an under floor fuel tank (80L)

Last week I was going to sea with a mate and when we pulled up for fuel he said I’ll get this one. He is my normal deckie and we share expenses.

Enough of that, I think (I’m sure) he put to much fuel in.

We headed to Gymea ramp the I got a phone call that terminated the day

The last couple of days have been hot, with today touching 40+

The wife tells me she can smell petrol near the boat.

I go to investigate and yes there is fuel dripping out of the centre/lower bung holes.

I take cover off inspect the bilge area and yes petrol dripping from joins in pipe that leads from fuel tank to filler.

I lean over the back of boat, undo fuel cap, remove and a at least a good two litres of fuel erupts/gushes out.

I know the reason and understand fuel expanding etc etc, but would this be considered normal ?

I ask this question only because I thought there would’ve / should’ve been a release valve or something to overcome this happening.

Thoughts, etc (Please)


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[ericcs]

your fuel tank should have a breather pipe for that reason. maybe yours is blocked?

[Bremic]

As above, I have filled the tank and had it expand and come out of the breather, but it shouldn't be leaking anywhere else.

I would have thought any boat with an underfloor tank would have a breather. Maybe yours is blocked?

[Dignity]

Blocked breather most likely cause, could be mud wasps, ants anything or possibly even a baffle inside the tank has come loose and blocking it from inside the tank. Start from the breather end first. Also every 4 years or so years I replace the lines from the fuel tank to the filter and to the breather as I find they go hard and I also replace the fuel line to the motor as the lining can start to breakup. Tightening the fittings will do little to alleviate your problem if the line has gone hard.

[Noelm]

Some boats that have the filler in the motor well area can have a problem, the filler is lower than the vent, so, any expansion gets pushed up the filler before it can exit the vent, that said, the filler should not leak, regardless of fuel level.

[Fed]

If the breather was blocked the motor would stop running.
You might have one of those new fangled anti pollution breather valves.
They stop fuel fumes escaping into the atmosphere but still allow air into the tank to displace the fuel as you use it.
I think they have a preset blow off of just a couple of psi but that wont happen if you have a leak in the system like yours.

[shakey55]

Some boats that have the filler in the motor well area can have a problem, the filler is lower than the vent, so, any expansion gets pushed up the filler before it can exit the vent, that said, the filler should not leak, regardless of fuel level.

Yes my filler is lower than the vents.

Note to self ‘don’t fill tank after use’ wait until going out on next trip.


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[Noelm]

Kind of guessed that was the case, it's pretty common, fuel expands right up to the filler before it reaches the breather vent, but, as mentioned, the tank shouldn't leak anywhere, regardless of how much fuel is put in.

[stevej]

Yes my filler is lower than the vents.

Note to self ‘don’t fill tank after use’ wait until going out on next trip.


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other argument is if the tanks are full less air can cool in the tanks and leave condensation behind
all a trade off of how often you use it and either the fuel going off or condensation building up in a empty tank

[Chris Tucker]

There are new EPA rules on their way (following US example). That will require tanks and breather systems to allow for 5% increase in volume due to temperature change without releasing fumes or liquid. Not an issue on old boats as it won’t be retrospective but is going to effect the capacity of fuel tanks in new boats as it basically means the tanks will be set up to only fill to 95%.

A lot of boats already come with stickers saying not to fill to capacity and then leave boat.

[Moonlighter]

Yes my filler is lower than the vents.

Note to self ‘don’t fill tank after use’ wait until going out on next trip.


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I really hope you are going to find where that leak really came from, and repair it so thta it cannot posisbly ever happen again.

There is simply no way I would be happy to know that fuel could escape into the bilge regardless of how.

Please dont just leave it.

[Moonlighter]

There are new EPA rules on their way (following US example). That will require tanks and breather systems to allow for 5% increase in volume due to temperature change without releasing fumes or liquid. Not an issue on old boats as it won’t be retrospective but is going to effect the capacity of fuel tanks in new boats as it basically means the tanks will be set up to only fill to 95%.

A lot of boats already come with stickers saying not to fill to capacity and then leave boat.

Quite a few boats have been fitted with overflow tanks (catch cans) now for many years.

My 2010 Surtees has a enclosed tank (like a catch-can) up under the gunwale, and the breather hose runs from the fuel tank into the bottom of this tank. The breather line then runs feom the top of the catch can to the external hull fulling. At a guess I would say this tank holds about 1 litre.

So if the fuel expands from the main 5ank into the catch can, only fumes can escape out the brearher line, no raw fuel unless the catch can fills right up.

If some liquid fuel gets up there, when fuel is used from the tank or it cools down, the fuel in the catch can runs back down int the tank.

Probably not much of a modificaion to this system to comply with the potential new rules.

i do already hear of problems with these new tank rules in the USA. Even the plastic 25l tanks have to comply, no breather valves in the caps ...... causing all sorts issues. There is already a booming market in replacement caps that are the old style.

[Noelm]

I had a 25l plastic tank that was only vented when the hose fitting was attached, if disconnected on a hot day, it used to expand like me after Christmas lunch, and during cold weather if would shrink to such an extent the sides would crinkle.

[Cape Crusader]

G'day
I don't know if it's relevant in this case but an issue I have had before is when the attitude of the boat (bow up or down) can impact the operation of the breather. Eg my last boat had 2 breathers but both at the stern end of the tank, when I parked it in our drive with the bow up it meant that the vapor space was trapped at the bow end of the tank with no where to go. When the temperature rose the vapour/air mix would expand (a great deal more than the liquid fuel) and push fuel up the breather and filler pipes, spilling a lot of fuel. I've heard of this happening to others also.
Our current boat has tank breathers at the front of the tanks so I always ensure a slightly bow up position in the shed.
Cheers
Rod