Fuel Tank Leaking

[DIRTY ROCK STAR]

Guys wondering if anyone has had similar happen or can point me in the right direction.

my comp rig runs a 100 series petrol sub tank for the last 5 yrs.
filler neck is from a late model unleaded 4runner.

last yr at tuff truck and now in my mates shed it is pressurised or something and fuel is spilling out the filler neck.
is this a blocked return line or something else?

The tank at the moment would be maybe 1/2 full at best i think and is dribbling out fuel. i tried to open the cap and let the pressure out but it pushed out too much fuel so i had to put it back on as i dont want his shed being too messy.

is this a blocked return line? is the system somehow pushing back pressure?
truck starts and runs fine but its costing me a fortune in premium unleaded, also the chance of a fire is real and concerning.

cheers

Twon

[turbo gu]

Have you got a breather connected to it?
Return is only from the motor.

[chimpboy]

Pressurising usually means it's not venting. If you don't have a breather then that could be an issue. Some older vehicles have a vent in the fuel filler cap; you can try leaving the cap off or having a small hole in it.

I had a car that was fuel injected but was still old enough to have a vented cap. It would build up pressure if you had a normal cap on it but there is no way it would actually spew out fuel just because of pressure build-up. Your problem sounds pretty strange to me, especially if the tank is only half full. In theory if that is the case then when you take off the cap it should just release vapour not liquid fuel. Is the filler pipe at the highest point of the tank?

Can you describe the overall set-up a bit more? It might help. Has anyone dicked around with it?

[91Mav]

The tank is supposed to vent through a charcoal canister which can get clogged. Check the canister and give it a clean along with the lines. This is usually to let air IN the tank though.

I have no idea why your tank would be getting pressurised. Like Chimpboy said, it's even more strange that fuel would come out the filler. Your filler must have hose running to the bottom of the tank?

[SIMMO84]

Does the filler go into the top of the tank? Not half way down? I'd say breather.

[DIRTY ROCK STAR]

i dont think there is a charcoal canister.
the filler goes pretty well into the top of the tank. the end of the filler is atleast 300mm above the top of the tank.

for the first 3 years or more it had no issues.



the return i meant is like a breather line thing. there is a small line that comes up off the tank to the filler neck.

[-Scott-]

i dont think there is a charcoal canister.
the filler goes pretty well into the top of the tank. the end of the filler is atleast 300mm above the top of the tank.

for the first 3 years or more it had no issues.



the return i meant is like a breather line thing. there is a small line that comes up off the tank to the filler neck.

I can't explain why it's only recently started (have you changed the filler cap, or is the vehicle now parked differently?), but everything points to the tank not venting properly.

The small line up the filler neck is (afaik) a breather to let air out of the tank as you fill, without rushing back up the filler pipe and bringing fuel with it.

A charcoal cannister is to catch the fuel vapours from the tank vent; as air expands it pushes out through the cannister, and the fuel vapour adsorbs to the charcoal. When the engine starts (and under the right conditions) the cannister is opened to manifold vacuum, and the vapour is (supposedly) drawn into the intake and burned. If you don't have a charcoal cannister then I guess the tank doesn't have a functioning venting system, although that still wouldn't explain why the problem only recently started.

[montana]

mr twon what is your set up, tank ,pump,fuel rail ,return to tank. anything else ? could just be a bit of moisture with mud/dust blocking the cap from venting.

[Wozza244]

Time for a fuel cell mate.

[DIRTY ROCK STAR]

could be time for a cell.

yeah thats basically it. intank fuel pump and return line. using solid lines along chassis.
then at filler its a basic sort of setup off a 4runner. using solid and rubber lines to tank and then the vent back up to filler.
I will check the cap etc.

But if it should vent from the cap it is, but fuel is coming out with it which sucks more then grimace on prom night.

[turbo gu]

It sounds like you dont have a breather at all??

If the vents run back to the filler neck that is only for filling up the tank not a vent for when the tank is sealed. Is the vent to the filler neck around 10/15mm in diameter?

[DIRTY ROCK STAR]

yeah the vent is about that diameter.

i wonder how a 100 series landcruiser tank normally vents then?
EDIT
through a carbon canister, but where does that fit into the plumbing?

[turbo gu]

I would say the connection to the charcoal cannister would possibly in the filler neck assembly or some other bit of plumbing that you dont have after using the 4 runner filler.
Is there any small diameter hoses on the filler neck you can vent out of?

[DIRTY ROCK STAR]

yeah thats what i am thinking might be the quick fix.
a filter or similar there to fix it and let it vent.

but what would stop it just pouring fuel out like it is now?
it is pushing fuel back out the filler cap still.

[loosecanon]

So just to be clear DRS, this is happening when the car is stationary?
I had something similar but on a 60 ( maybe different as it was a carbie) and this was due to the breather line not being connected properly

[lay80n]

There should be a breather on it, there was when we put it in a few years ago, but who knows what you have done with it, possibly used it to tie up some back packers If you want a hand you have my number mate.

Layto....

[chimpboy]

Even if there's no breather, it still sounds a bit weird to me to have fuel coming out of the filler. A big whoosh of vapour maybe, when you open the cap, but not fuel. It doesn't add up for me.

I have one idea, it might be stupid but... could the in-tank fuel pump or some of its plumbing have come loose or disconnected or something in such a way that it is picking up fuel and then pumping it out through the filler neck? Or could something similar have happened with the return or something? It's probably a long shot but it might be worth a look..?

[80's_delirious]

the 100 series tank should have a small breather tube coming from the cover plate of the in-tank fuel pump, it normally has a thin rubber tube running up into the chassis crossmember to vent it. I believe they can get clogged with mud causing the tank to pressurise with vapours.

As for it spitting fuel out of the filer cap, it sounds like your filler pipe is not coming from the highest part of the tank? or dips down from the tank before going up to the filler cap?

[montana]

I have one idea, it might be stupid but... could the in-tank fuel pump or some of its plumbing have come loose or disconnected or something in such a way that it is picking up fuel and then pumping it out through the filler neck?

not stupid, the pump could airated the fuel to vapour causing pressure.

[stilivn]

For those that cant figure how the fuel is coming out the filler neck, i would say the fuel is traveling up the smaller hose not the large one. I may be wrong but i was under impression that hose was how the pump knew the tank was full.

[turbo gu]

[quote="chimpboy"]Even if there's no breather, it still sounds a bit weird to me to have fuel coming out of the filler. A big whoosh of vapour maybe, when you open the cap, but not fuel. It doesn't add up for me.

quote]

Its quite possible that it will blow out alot of fuel.
had it happen to me a few times over the years on various cars.

[DIRTY ROCK STAR]

There should be a breather on it, there was when we put it in a few years ago, but who knows what you have done with it, possibly used it to tie up some back packers If you want a hand you have my number mate.

Layto....

cheers wigga.
there wasnt a hose style breather though? maybe its ontop of the tank and clogged?

i will throw up a photo.

[chimpboy]

I may be wrong but i was under impression that hose was how the pump knew the tank was full.

If you mean the pump at the bowser... no, bowsers have a small tube in the dispenser that senses when the tank is full and cuts off the flow.

Its quite possible that it will blow out alot of fuel. had it happen to me a few times over the years on various cars.

Fair enough, I guess odd things could happen with a sudden release of pressure; it's just not something I've seen.

I am just being cautious about the "pressure" though explanation as it is mentioned in the original post but it seems like an assumption of a possible cause not a definite observed symptom, and sometimes these things can be a bit of a red herring.

[Bumpy45]

The only way that fuel can come back up the filler is if the point that the filler tube is below the actual fuel level and that the filler is completely sbmerged in the tank. Any air that is in the tank will blow out and not carry much fuel.
Emty the tank, do a calculation to find the tanks volume then fill it. This will tell you if you are actually filling the tank completely. I would hazzard a guess that where the filler hose enters the tank it has gone in deeper and sits under the fuel level.
Sure a breather should vent the pressure, but this is a secondary issue.
You mentioned that the tank is half full can you look down the filler and see fuel in the tube? if you can then the tube is in too deep.

[DIRTY ROCK STAR]

[DIRTY ROCK STAR]

Thats a pic ofthe setup as it is.
the filler opening is above the tray you can see.

The tank may be full beyond the low point of the filler neck. but i wouldnt have expected that to cause fuel to flow out?

That is standard position for 100 series subtank filler, unless its different because it would normally flow into a main tank??

[chimpboy]

The tank may be full beyond the low point of the filler neck. but i wouldnt have expected that to cause fuel to flow out?

Seeing your photo now, I think it could if there was a pressure build up. Pressurised gas will be above the liquid fuel in the tank and the filler hose becomes the best way for the pressure to get out... although I would still expect the tank to have to be quite full for this to happen.

You need a breather/vent at the top of the tank. Is there any threaded hole or anything going spare that you can use for this job? then you can just run a bit of rubber hose from it to a little filter that vents to air and forget about it. I would not bother with a charcoal canister in a comp rig.

[DIRTY ROCK STAR]

will investigate the breather options soon.
its away getting a lick of paint now.

[Modified Toy]

You could use one of these a roll over valve used as a breather but in the event of a roll shuts off

http://www.vpw.com.au/productgroup.asp? ... GrpID=5519" onclick="window.open(this.href);return false;

[DIRTY ROCK STAR]

Champion idea!