Vent to Nowhere

[gcarm]

Hi,

I have a small metal tube that is coming off the filler neck to my fuel tank. Its close to where the fuel cap screws in.

I understand the purpose of this tube is to allow air to escape when filling the tank. Also, as fuel is consumed, it allows air to enter the tank so there will be no problems with a vacuum being created in the fuel tank.

My question is - do I need to connect this tube to anything, or does it just hang there? Its about 100mm long and angled down towards the bottom of the boot.

I assume when I'm filling the tank that the nozzle cutoff will stop the fuel level from rising to a point where fuel may travel down the tube???

Cheers,
Greg

[stephen low]

Greg

The tube does need to be connected somewhere.

The fuel filling assumption should be taken as wrong and there is always the chance of over-filling. Where does that fuel go, into your boot if not redirected.

The prior owners of my unfinished kit had bought the standard steel GF fuel tank. Beside the main fuel filling neck into the tank is a smaller tube to which my upper overflow pipe is connected.

Obviously both tubes and attached pipes will fill as you overfill the tank but the additional volume helps limit potential for complete overflow at the external fill point. As you say too, it allows air reventing back into the tank and no fuel escape into the boot by the connecting smaller tube.

If your tank doesn't have a second tube, you could direct the overflow tube to the outside world, then you don't end up with a boot full of fuel with all the risks and issues that will bring.

It's a must have ... not a desirable option!

Cheers

Steve

[gcarm]

Steve,

I'm using an RCI off the shelf tank. It has the main outlet, a return and a roll-over vent.

I guess I could connect it to the return using a 'Y' connector. Otherwise, as you mentioned, just pipe it outside the vehicle.

Thanks for the advise.

Cheers,
Greg

[C5GTO]

There's a good solution to gas tank venting provided by Morris shown in pictures here: Gas tank becoming pressurized???

I used it as a guide in fixing the gas tank venting on my Cobra. Bottom line, it worked well. The addition of a ground for the fuel cap was also a great tip.

[xb-60]

Originally Posted by gcarm

....just pipe it outside the vehicle....

Greg - absolutely, definitely (and legally), do not pipe the overflow outside (ie dumping to the ground) unless you want to be on the 6 0'clock news

There are a number of issues here, not least of which is your own safety.

Here are several pictures that should indicate what sort of breathing and provision for overflow that you need....


Firstly, a picture showing the general arrangement of the pipes/hoses, clearly showing the overflow hose connected just below the fuel filler.....





Next one shows more clearly the fuel tank breather hose (the small diameter hose that loops up quite high) as well as the fuel return (to the tank, it's the larger diameter hose)....





Lastly, this one shows the plumbing underneath. You can see the overflow hose (the larger hose) connected so that the fuel overflow returns directly to the tank. It also shows the breather hose (the smaller hose) which goes forward to the charcoal canister mounted somewhere near the engine.





Also extremely important is to install an earth strap to electrically connect the fuel filler (remember it's metal, so it's electrically conductive!!) to the chassis (earth).
That could save you and your car from catching fire.


I hope that helps a little.


Cheers!
Glen

[gcarm]

Glen,

Thanks for the detailed explanation with photos.

So two things I need to do:
1) Pipe the filler overflow tube back into the tank
2) Place an earth strap from the filler neck to the chassis

One thing I fogot to mention - the tank has a rollover valve installed which is also used to 'vent' the tank. I have connected this to the charcoal cannister which I believe is where it should go.

So its really only the overflow when filling that I need to be concerned about. I'm thinking it may be best to feed the filler overflow tube into the tank vent/rollover outlet via a 'Y' connection. Does this make sense?

Cheers,
Greg

[Morris]

Any and all vents on a fuel system need a check valve.