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#134705 - 06/05/13 04:59 PM petrol tank problems
nick w Offline

Talk Morgan Expert

Registered: 31/03/09
Posts: 2020
Hello all, I'm wondering if any of you have expertise relating to my petrol tank problem.
I have a 2005 roadster with what I believe to be a stainless steel fuel tank. I know stainless is relatively stiff and harder to weld - but the top seams have lifted a little. This manifests initially as the smell of petrol, particularly when the tank is full, ofcourse. Anyway it soon turns into a leak. I have twice now sealed the seam (araldite) which works but then a new leak appears in another part of the seam. I'm talking fumes really, no pools of petrol anywhere; although if I fill the tank I can force damp out by shaking the car. Only the top seams. Is it that the tank was never welded properly or.....
when I open the filler I hear a rushing sound rather like in the old days when the pinhole that used to be standard in filler caps got blocked and a vacuum would form. But I'm wondering if mine is fumes rushing out as the tank is pressurisd isn't it? There is a plastic box and a metal cylinder mounted above the tank....I'm wondering if there is an exit filter route which may be blocked. If my tank is completely sealed and the petrol expands it could force even good welding apart could lt?
Hoping that all makes sense...........any ideas?
nick

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#134708 - 06/05/13 05:19 PM Re: petrol tank problems [Re: nick w]
DaveW Offline
Roadster Guru
Member of the Inner Circle

Registered: 11/12/08
Posts: 17256
Loc: South Yorkshire
I think it was during my trip to Mulfab that in conversation I discovered that chassis flex and therefore the twist of the wood under the tank can cause seams to fail. It was a known problem on racing Roadsters, but less evident on road cars. Give Mulfab a ring, they will know where the tanks usually fail. I doubt that pressure would break a weld, although you never know. You could test opening the filler by cable tying an inflated rubber glove around the neck under the cap. Then release the locking cap through the glove, and watch whether the glove gets bigger or smaller...............
_________________________
DaveW
2005 Corsa Red Roadster S1
2016 Saffron Yellow (Narrow) Plus 4

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#134729 - 06/05/13 07:47 PM Re: petrol tank problems [Re: DaveW]
Lecat Offline
Learner Plates Off!

Registered: 03/01/13
Posts: 423
Loc: Northern Sweden
Nick, I think your thoughts about the welds and the 'exit filter route' are correct. Two things springs to my mind.
First: As you write, welding stainless steel can cause the material to become brittle (not uncommon on exhausts). Periodic change in pressure in the tank could lead to material fatigue and eventually a crack (experience I have from normal steel tanks Dave).
Second: The rushing sound could be air rushing in due to vacuum build up during driving. The reason could be a faulty roll-over-vent valve - I've had that problem recently and solved it temporarily by just bypassing it with an extra tube.
I guess that your problem could be the result of the pressure changes and perhaps a weak weld that has finally developed a crack.
Try to bypass the roll-over-vent valve to check the vacuum theory. If you want to check for a crack you can use chalk on the weld (baby powder could work) and shake the car. The crack should appear as a dark line or spot.
Hope this helps a little - wish you good luck...


Edited by Lecat (06/05/13 07:50 PM)
_________________________
-99 4/4, 1.8 Zetec, Indigo Blue, 2-seat, Suplex RS
-04 Citroen Pluriel, 1.6 Sensodrive, Met Orange

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#134774 - 07/05/13 05:35 AM Re: petrol tank problems [Re: Lecat]
nick w Offline

Talk Morgan Expert

Registered: 31/03/09
Posts: 2020
Thanks Dave and Thomas.
Clever idea about the glove Dave, I'll do that.
Thomas, what does the roll over vent valve look like? Is it he metal cylinder attached to the wooden crossbar above the petrol tank? I assume the black plastic box on the left is the charcoal filter....which incidentally has a pipe coming out of it which looks as if it ought to have a tube attached but never has had.
Nick

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#134784 - 07/05/13 07:44 AM Re: petrol tank problems [Re: nick w]
Lecat Offline
Learner Plates Off!

Registered: 03/01/13
Posts: 423
Loc: Northern Sweden
I will send you an image if you could PM me your email...
_________________________
-99 4/4, 1.8 Zetec, Indigo Blue, 2-seat, Suplex RS
-04 Citroen Pluriel, 1.6 Sensodrive, Met Orange

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#138664 - 04/06/13 05:46 PM Re: petrol tank problems [Re: Lecat]
nick w Offline

Talk Morgan Expert

Registered: 31/03/09
Posts: 2020
Hello all,
My petrol tank woes continue. Thanks to Dave W's brilliant rubber glove idea I've ascertained that the hissing which sounds like air entering the filler, is in fact air escaping. So the tank is under pressure after the engine runs, and it seems more pressure as the tank empties. Does anyone know if it should be pressurised? I have sealed the tank now so no longer have the smell but it seems to me the problem is still there in essence, just waiting to give me grief soon.....
Any ideas?
Nick

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#138673 - 04/06/13 07:46 PM Re: petrol tank problems [Re: nick w]
DaveW Offline
Roadster Guru
Member of the Inner Circle

Registered: 11/12/08
Posts: 17256
Loc: South Yorkshire
Here's one solution:
http://www.demon-tweeks.co.uk/motorsport/fuel-tank-vent-valves/mocal-fuel-tank-pressure-relief-valve

Quite a bit on the internet about positive pressure but I haven't found a sensible solution yet............

A blocked carbon canister gets a mention occasionally.
_________________________
DaveW
2005 Corsa Red Roadster S1
2016 Saffron Yellow (Narrow) Plus 4

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#138769 - 05/06/13 01:17 PM Re: petrol tank problems [Re: DaveW]
Lecat Offline
Learner Plates Off!

Registered: 03/01/13
Posts: 423
Loc: Northern Sweden
As Dave writes, it's hard to find any sensible information on excessive gas tank pressure. But, it's pretty clear that, if there is a pressure build up for any reason, the vent valve doesn't release it until it reaches a certain level - how high I don't know...
One thing makes sense in your case: 'more pressure' when tank empties must be that there is room for a larger volume of gas - not likely higher pressure.

(read Tom Russ' comment: http://www.jag-lovers.org/xjlovers/xjfaq/tankgasp.htm)


Edited by Lecat (05/06/13 01:19 PM)
_________________________
-99 4/4, 1.8 Zetec, Indigo Blue, 2-seat, Suplex RS
-04 Citroen Pluriel, 1.6 Sensodrive, Met Orange

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#138770 - 05/06/13 01:35 PM Re: petrol tank problems [Re: Lecat]
nick w Offline

Talk Morgan Expert

Registered: 31/03/09
Posts: 2020
Thanks chaps, I really appreciate your input.
Nick

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#138815 - 05/06/13 04:46 PM Re: petrol tank problems [Re: nick w]
The Phantod Offline
L - Learner Plates On

Registered: 03/11/10
Posts: 167
Loc: Los Angeles
Your fuel tank should not be pressurized to any extent. Fuel returning to the tank is heated in the engine compartment and will try to cause a pressure rise in the tank. When the car is parked, the trapped fumes in the tank are supposed to be scavenged by the canister, but with the engine running the fumes are supposed to be fed into the intake. Pressure build-up while running is indicative of some problem with the venting/scavenging system.
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'65 +4 four seater

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#138820 - 05/06/13 05:03 PM Re: petrol tank problems [Re: The Phantod]
nick w Offline

Talk Morgan Expert

Registered: 31/03/09
Posts: 2020
It's hard to know if the pressure builds up during running.but it certainly does while parked . I'm beginning to wonder if my charcoal cannister is blocked although I can blow through it ok......
Nick

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#138896 - 06/06/13 07:00 AM Re: petrol tank problems [Re: nick w]
John V6 Offline

Member of the Inner Circle

Registered: 21/07/07
Posts: 13028
Loc: Suffolk
Normally the canister only vents at higher revs than idle.
Mine has a solnoid valve on it to do that.

My +4 will build pressure and after idling if you open the tank you can hear it escape
_________________________
JohnV6
2006 Indigo Blue Roadster S1

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#138917 - 06/06/13 09:48 AM Re: petrol tank problems [Re: John V6]
nick w Offline

Talk Morgan Expert

Registered: 31/03/09
Posts: 2020
John, where is the solenoid please?
Ta
Nick

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#138937 - 06/06/13 11:47 AM Re: petrol tank problems [Re: nick w]
John V6 Offline

Member of the Inner Circle

Registered: 21/07/07
Posts: 13028
Loc: Suffolk
Mine is a Rover T16 Engine. You can see it in this dwg it is above the canister in the dwg.
http://www.rimmerbros.co.uk/Item--i-GRID004967

I guess on any car there is one either on the canister or the inlet manifold


https://sites.google.com/site/morganatica/engine/rover-t16
_________________________
JohnV6
2006 Indigo Blue Roadster S1

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#138940 - 06/06/13 11:58 AM Re: petrol tank problems [Re: John V6]
nick w Offline

Talk Morgan Expert

Registered: 31/03/09
Posts: 2020
Thanks John, I don't have it on the cannister so I'll go looking on the inlet manifold.
Looking at the link it seems the assembley is 12 for your car. I've been quoted 178 + vat for the charcoal cannister for mine! Plus the rollover valve is 77 plus vat........
Progress......

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#138943 - 06/06/13 12:01 PM Re: petrol tank problems [Re: nick w]
John V6 Offline

Member of the Inner Circle

Registered: 21/07/07
Posts: 13028
Loc: Suffolk
Try e bay for breakers parts
_________________________
JohnV6
2006 Indigo Blue Roadster S1

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