Reverse petrol leak

[Spout]

Some of you may remember that I have a problem with a strong petrol smell coming from my 02 Adv whenever its parked up warm (especially in the confined space of my garage).

There are no apparent leaks, and all fuel/breather lines/’o’ rings/filter have been replaced. The smell has been 100% traced to the ‘expansion’ breather. So I figured the petrol is getting warmed up by the hot engine and the breather working properly. So nothing to fix, then.

The smell of petrol was cured by connecting the breather to a length of garden hose (suitably affixed around my garage walls, which then exits through the outside door), every time I park up the bike.

This has been working fine for nearly a year now. But last night one of the garden hose connectors came loose and I was reminded of the appalling amount of fumes my breather kicks out.

Something aint right.

So I was sat in the quiet of the garage having a ‘thinky’ about it.

Every 10 to 15 seconds there was a gurgling in my tank. Air is coming in and bubbling up.

Now this has me confused. How can air get in, without petrol leaking out? And where is it coming from?

The heat of the engine is causing the pressure – once cool there’s no smell.

It must be from a source of air with enough pressure to push past gallons of petrol (infact the fuller the tank the less the smell – seems logical).
So it can’t be from outside the tank.
Still bubbles with filler open, so isn’t being sucked in.

Must be from inside the fuel lines? Is there any air in there? And where from?

Any ideas?

It appears I’ve got a leak that’s working in reverse.

 

[jez]

does that mean you'll never have to buy petrol again if so can I have a leak like that too

 

[cookie]

all kinds of possibilities from the breather hoses on inside of fuel pump bulkhead i'd imagine.

might be worth stripping tank down & inspecting + renewing pipe clamps?

 

[Steptoe]

As cookie says - you have two lines attached to the fuel pump and run through the tank that could let air in, or fumes and petrol out - the breather, and overflow .

Check the connections inside - they're fixed with very small BMW crimp connectors, if your going to replace them with re-usable connectors , i'd find the connectors first, becuase they are an unusually smal size .

 

[Deleted account 220427002]

could it be the o ring on the tank- petrol cap or the fuel pump seal?

when lid closed can you blow up the hose?

and then with the lid open

what do i know...

 

[Spout]

Cheers chaps.
All fuel lines and connectors have already been replaced.

The hot engine is warming 'something' up which is 'forcing' air 'somehow' into the tank. Hence my over active breather.



Inspiration:

Air must be being pushed back out of the petrol pick up.

So where is the air coming from? There are no actual leaks in the fuel lines (I'd be able to smell a leak right? and with my breather isolated there's no smell).
Is my fuel filter full of air?
Air collecting in the fuel pump somehow?
I suspect it's the fuel lines to/from the fuel regulator that are getting warmed up (they're the only ones close enough to the hot engine?)
But why would there be air in them?

Cheers again.

 

[Steptoe]

Cheers chaps.
All fuel lines and connectors have already been replaced.

.

I'm not talking about the fuel lines - but the breather and drain pipes, which run through the tank via the pump housing

 

[Spout]

I'm not talking about the fuel lines - but the breather and drain pipes, which run through the tank via the pump housing

Yes Steptoe, these have also been replaced. And air from these would only be at atmospheric pressure - not enough to force into the tank. Certainly got me thinking!

 

[cookie]

just been mulling over this drawing

if air is getting into the tank, below the petrol level, but petrol is not leaking out, it must be coming in via one of the pipes at the bulkhead.
the only one i could see doing that without leakink fuel out, is the injection fuel return pipe.

that could theoretically pick up air & dump it in the tank i think

i've not played about with the plumbing arrangements immediately before & after the injectors [behind the airbox], so i don't know where that is likely to happen.

edit: i wonder if it's possible that the regulator is capable of bleeding air into the system? seems a bit of a long shot, but there aren't too many options.

 

[Mouse]

Are you sure you've got this the rigth way round? Perhaps the tank is hot after a ride, and when you park up it starts cooling - therefore the pressure inside drops and it sucks air into the tank through one of the breathers.

No experience of a GS doing this but I do know my girlfriend's GPz500 makes a distinct whining noise as it's cooling down, the noise is caused by air being sucked through a breather somewhere. Opening the filler cap stops it instantly and you can hear a small rush of air when you do so.

Is a simple solution to the problem just to pop open the filler cap for a moment when you park up?

 

[Spout]

Are you sure you've got this the rigth way round? Perhaps the tank is hot after a ride, and when you park up it starts cooling - therefore the pressure inside drops and it sucks air into the tank through one of the breathers.

No. Air is definately being expelled out of the breather.
If I put the end of the breather in a glass of water it bubbles (constantly near the surface, and at a slower rate the deeper in - so I could calculate the pressure I suppose!)
With filler cap open air is still being forced in (but obviously the breather stops bubbling).

 

[riverking]

There doesn't seem to be anything happening that shouldn't happen (if I've understood it correctly), the problem seems to be the excessive rate or degree by which it is happening.

If the culprit is heat causing vapour rather than an air ingress, then that would point to excessive heat reaching either the tank or fuel lines or both.

Are you certain that during this work either a fuel line has not been routed closer to a heat source that is correct, or is there any sort of insulator or heat deflector that has been misplaced. (Sorry Spout I don't know the layout under the tank, others obviously do}.

Again I do not know the system, but if there was any type of (intentional) downstream residual pressure after the pump, and this was being allowed to dissapate backwards through to the tank rather than being held or dissapated via another route, this would have the same effect (ie. some kind of failed non-return device within the downstream fuel system).