mk1 pressure in tank?

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accyimp
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mk1 pressure in tank?

Post by accyimp » Wed Apr 04, 2018 9:17 pm

Hope this isn't too stupid a question, here goes -
Should there be vapour pressure when you open the fuel filler cap after the engines run up to temperature? I don't want to be searching for a solution if there isn't a problem. MK1 injection.
MOT getting nearer?
Cheers
Andy.



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Re: mk1 pressure in tank?

Post by mark1gls » Wed Apr 04, 2018 10:57 pm

Normal for some pressure in the tank when taking the filler cap off in an fuel injection car.


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Jack92
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Re: mk1 pressure in tank?

Post by Jack92 » Thu Apr 05, 2018 7:30 am

As Mark said normal, I get it in my Mk2. Don’t get me wrong it’s not like a huge amount but there is some


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Re: mk1 pressure in tank?

Post by accyimp » Thu Apr 05, 2018 7:28 pm

Thanks for that gents!
Andy.



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james butler
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Re: mk1 pressure in tank?

Post by james butler » Sat Apr 07, 2018 2:42 am

how does it pressurize? a vacuum i can understand as the fuel level drops and air cant get in from a blocked breather.


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Jack92
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Re: mk1 pressure in tank?

Post by Jack92 » Sat Apr 07, 2018 6:49 am

james butler wrote:how does it pressurize? a vacuum i can understand as the fuel level drops and air cant get in from a blocked breather.
To be honest I’ve barely taken any notice of it, it might well be vacuum pressure. I only here it when I’m listening for it lol


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Re: mk1 pressure in tank?

Post by chopperoli » Mon Apr 09, 2018 3:15 pm

If you don't have the ventilated fuel filler cap, then the tank vents to atmosphere via a gravity valve up inside the arch near the filler neck. from there it goes down to a long thin tube on the tank which might be blocked.

There should not be much pressure in the tank at all, that could be dangerous



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Re: mk1 pressure in tank?

Post by accyimp » Mon Apr 09, 2018 8:56 pm

Ill get it up on a ramp tomorrow and check the pipes in r/o/s arch - and it may well be a vacuum? but there is a definite difference in pressure to atmospheric - positive or negative



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Re: mk1 pressure in tank?

Post by blakey » Mon Apr 09, 2018 10:03 pm

It's normal - there's a very good k-jet guide on the Mk1 Golf Forum:

15.1.2 The Fuel Tank
The fuel tank is the obvious place to start in any fuel system explanation - unlike the tanks on early carburetor fuelled engines it is a sealed unit. This allows the natural gassing of the fuel to aid delivery to the pump by slightly pressurising the tank It may be noted that when the filler cap is removed, pressure is heard to escape. Filler caps are no longer vented as previously found.

https://vwgolfmk1.org.uk/forum/index.ph ... ade-easy_2

It's not noticeable on my Scala, but very noticeable on my previous GTX.


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chopperoli
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Re: mk1 pressure in tank?

Post by chopperoli » Mon Apr 09, 2018 10:39 pm

'slightly pressurising the tank'



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Re: mk1 pressure in tank?

Post by accyimp » Tue Apr 10, 2018 8:48 pm

Thanks all :)



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Re: mk1 pressure in tank?

Post by accyimp » Tue Apr 10, 2018 8:55 pm

Thanks very much for the link - will also help with the high tick over of 1500rpm! Some very good info.
Cheers
Andy.
blakey wrote:It's normal - there's a very good k-jet guide on the Mk1 Golf Forum:

15.1.2 The Fuel Tank
The fuel tank is the obvious place to start in any fuel system explanation - unlike the tanks on early carburetor fuelled engines it is a sealed unit. This allows the natural gassing of the fuel to aid delivery to the pump by slightly pressurising the tank It may be noted that when the filler cap is removed, pressure is heard to escape. Filler caps are no longer vented as previously found.

https://vwgolfmk1.org.uk/forum/index.ph ... ade-easy_2

It's not noticeable on my Scala, but very noticeable on my previous GTX.



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Re: mk1 pressure in tank?

Post by moser » Tue Apr 17, 2018 11:22 am

Noticed this on mine when i got home from work the other day. I had perviously noticed a petrol smell from the rear the other day so i assume it has a leak of some sorts, the opposite side to the filler neck the tank looks damp ish but not dripping. Then friday after a drive home from work it was hissing from the same area. Took the cap off and the pressure behind it was quite substanial. Dont ever remember it being that bad. I've parked it up for now and using my daily again. Something to add to the list and investigate in due course!!


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