Overflowing petrol filler pipe... how?

[Sorry if you get this, or similar, twice - I one earlier and I think it failed - that'll teach me to use Google Groups!]

I got a call from my neighbour today advising me that my girlfriends car (Mk IV Fiesta, 1.25L petrol) was leaking petrol... from the filler cap.

I couldn't get my head around how this could be, not unless she'd filled it right to the brim (it had been filled only at the weekend) and perhaps today's sunshine had increased the pressure such that it was now overflowing (to the tune of a drip every few seconds). But then it would really take some doing to fill it that much... right?

So, when I got home I removed the filler cap and indeed found the petrol level to be right at the top... I wondered if the camber of the road had anything to do with it so replaced the cap and drove to a flat spot. When I got there I checked again and the level had dropped (completely out of sight in fact) and so I returned to the original parking position... and the petrol was still nowhere to be seen.

I wondered if perhaps something had blocked the filler pipe and managed to keep the level high? And perhaps this blockage was now in the tank? But then surely this would have posed difficulties when she filled it... and the receipt shows a full tank (~30L) was I'm not so sure about the theory anymore...

I'm now thinking more along the lines of a trapped air bubble? (I notice the filler pipe travels vertically down from the opening for around 8" and then horizontally for perhaps 20" to the tank. There appears to be two pipes to the filler - I don't know where the other goes (/comes from).

Any ideas? I'm losing hair scratching my head on this one so your thoughts would be much appreciated!

Incidentally, for what it's worth, the filler cap is a lockable aftermarket affair - when we bought the car a few years ago the cap was found to be one of those temporary push-in affairs. Also, we occasionally smell petrol inside the car (in the boot mainly, near the filler) and this is usually shortly after filling the tank. I've always put this down to sloshing fuel in the tank/filler and the likely less-than-perfect fitting of the aftermarket cap (whose gasket I see is starting to perish) which might be letting the occasional splash out to the surrounding area.

Mathew

Reply to
Mathew Newton
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first off get a genuine cap

Reply to
Mrcheerful

Do you think that caused it? (or is it just a sensible step?)

I'm thinking the aftermarket cap might just be a coincidence (of course, this might the down to having read somewhere that the genuine article is something like =A354 and will come with a big fat Ford key...!)

Mathew

Reply to
Mathew Newton

they are not that dear, maybe 20 quid or therabouts. but if the aftermarket one does not breathe as it should ............ Worth changing, even if you get one from a breakers. other possibles might be something in the pipe, but I doubt it. If the tank was very full, parked to one side with fuel up the filler pipe, when the air above the fuel in the tank expands (as it always does, because fuel from an underground tank is much colder than above ground) it will then push the 'plug' of fuel further up the filler pipe, the cap is the weakest spot. bear in mind that fuel does expand a lot, and the fumes above it do too.

Reply to
Mrcheerful

A 15 degC rise gives you 1.5% extra. If you top it up & leave it in the sun it can leak out the top. But the smell's probably a crap filler cap..

Reply to
Duncan Wood

Mathew Newton expressed precisely :

If a bubble of air were trapped in the tank opposite the filler, combined with the fuel warming up after coming out of the ground - that would account for it overflowing. A quick drive round the block and the bubble moves to the filler neck.

Reply to
Harry Bloomfield

Dunno why it was too full in the first place but surely the level went down and stayed down because you used the fuel to drive?

Geo

Reply to
Geo

I only went 200 yards... :-)

I think the air bubble in the horizontal section of the filler pipe is sounding like the most feasible explanation. It may well never happen again, and besides I'll get a new filler cap which may provide a better seal to at least likely solve the occasional fumes-in-cabin issue.

Thanks everyone for the input,

Mathew

Reply to
Mathew Newton

I doubt this is related to the problem but I remember replacing my parents' Humber Sceptre locking filler cap with an aftemarket one. Apparently the original had a breather to let air into the tank as the petrol level dropped, the replacement didn't. Consequently as the petrol got used up, there was no way for air to replace it as the new cap was an airtight seal. The tank slowly imploded until it would hold no more than about 2 gallons.

If I hadn't removed the flattened tank and replaced it I would never have believed this could happen.

Gareth.

Reply to
Gareth Magennis
[...]

Oh, it sure can!

It was a "feature" built in to early Ford Granadas...

Chris

Reply to
Chris Whelan

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