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#513266 - 15/05/18 08:45 PM Vacuum from fuel tank
Craig Jezzard69 Offline
Learner Plates Off!

Registered: 27/03/17
Posts: 358
Loc: Oxon
I have been experiencing what I feel is an excessive equalisation of pressure when I remove my filler cap to refill the tank. I recently had a leaking tank replaced under warranty together with modification to a new roll-over valve in a new location. However there is still an alarming amount of suction when I take the cap off (when the tank is low) I know there will be some pressure differential, but my question is, how much is too much?
_________________________
Craig Jezz

2016 Morgan 4/4 Sports Sand (Wolf tuned)
2016 BWM 320d M Sport Xdrive

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#513267 - 15/05/18 08:56 PM Re: Vacuum from fuel tank [Re: Craig Jezzard69]
+8Rich Offline

Member of the Inner Circle

Registered: 15/12/09
Posts: 14847
Loc: Devon UK
As I have said before Craig I don't have any pressure build up in my tank in either direction but being older it will not be subject to the same environmental issues as yours.

This year however a couple of weeks ago when in for her MOT one of the checks was removal of the filler cap - so I wonder is it something Morgan specific or just a change in the rules.

Others in the trade on here will know.
_________________________
Richard
1999 Indigo +8






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#513268 - 15/05/18 09:15 PM Re: Vacuum from fuel tank [Re: Craig Jezzard69]
Craig Jezzard69 Offline
Learner Plates Off!

Registered: 27/03/17
Posts: 358
Loc: Oxon
Thanks Richard

I just filled it to the top with fuel, then opened the fuel cap when I arrived home after 10 miles, and now all seems fine.

But when I open the cap on an empty tank, there is a huge rush of air 💨 that lasts a few seconds

As long the tank doesn’t split / fail again (on the weak weld joints as some say) I’m happy. At least it doesn’t spray me with petrol anymore, the new roll over valve in a new location solved that.
_________________________
Craig Jezz

2016 Morgan 4/4 Sports Sand (Wolf tuned)
2016 BWM 320d M Sport Xdrive

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#513299 - 16/05/18 07:09 AM Re: Vacuum from fuel tank [Re: Craig Jezzard69]
ewn Offline

Talk Morgan Regular

Registered: 10/04/16
Posts: 659
Loc: NE Scotland
My car does the same, I’ve never routinely removed the cap just to see, only when I need petrol and I generally brim full the tank and refill when near empty.

I think I’ll start opening the tank before and after journeys to find out what makes a difference, it can’t be good for it.

Re. MOT, cap security has been a standard part of the test for quite a while, it has to fasten on and seal.

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#513314 - 16/05/18 09:18 AM Re: Vacuum from fuel tank [Re: Craig Jezzard69]
Craig Jezzard69 Offline
Learner Plates Off!

Registered: 27/03/17
Posts: 358
Loc: Oxon
Thanks Ewn

That’s good to know
_________________________
Craig Jezz

2016 Morgan 4/4 Sports Sand (Wolf tuned)
2016 BWM 320d M Sport Xdrive

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#513317 - 16/05/18 09:27 AM Re: Vacuum from fuel tank [Re: Craig Jezzard69]
NeilL Offline

Talk Morgan Sage

Registered: 16/10/12
Posts: 6390
Loc: Warks
Craig - for what its worth my 4/4 does not have this issue.

I agree with Ewn - it cannot be right for the tank to create this vacuum - surely it will cause distortion of the tank - or at least undue pressure on the welds/seals.

Might be worthwhile calling MMC warranty team?
_________________________
Neil
4/4 Saxe Blue 80th

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#513319 - 16/05/18 09:33 AM Re: Vacuum from fuel tank [Re: Craig Jezzard69]
Craig Jezzard69 Offline
Learner Plates Off!

Registered: 27/03/17
Posts: 358
Loc: Oxon
Thanks Neil

I’m waiting for the dealer to contact me this afternoon. This is weird as some do this & some don’t.....

Like I said, I’m not overly worried as long it doesn’t contribute to splitting the tank.

I will wait & see what they say this afternoon. If I’m honest I can’t see how much more they can do, they have pretty much changed everything.
_________________________
Craig Jezz

2016 Morgan 4/4 Sports Sand (Wolf tuned)
2016 BWM 320d M Sport Xdrive

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#513355 - 16/05/18 12:48 PM Re: Vacuum from fuel tank [Re: Craig Jezzard69]
ewn Offline

Talk Morgan Regular

Registered: 10/04/16
Posts: 659
Loc: NE Scotland
At least I know my tank isn’t cracked, it wouldn’t suck if it was idea

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#513377 - 16/05/18 05:08 PM Re: Vacuum from fuel tank [Re: Craig Jezzard69]
IvorMog Offline

L - Learner Plates On

Registered: 17/04/17
Posts: 204
Loc: Staffordshire
Do you notice a change in engine performance as the tank empties?

If there is a significant vacuum in the tank either your fuel pressure would be dropping or your fuel pump would have to work a lot harder to maintain the pressure at the regulator.
_________________________
Bob

1999 4/4 1.8 Zetec Silvertop

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#513398 - 16/05/18 06:05 PM Re: Vacuum from fuel tank [Re: Craig Jezzard69]
Craig Jezzard69 Offline
Learner Plates Off!

Registered: 27/03/17
Posts: 358
Loc: Oxon
No loss of performance Bob, not that I can notice anyway.

However, I friendly man at MMC has arranged for my car to be collected and checked over at the factory, next month.

It will feel very odd having an empty garage 😢
_________________________
Craig Jezz

2016 Morgan 4/4 Sports Sand (Wolf tuned)
2016 BWM 320d M Sport Xdrive

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