Long Post Alert Gravity Valve

LONG POST ALERT


Gravity Valve dilema… A few weeks ago my fuel tank developed a leak and I replaced the tank. While the leak was visible where it came from wasnt.


I replaced the tank as taking it off and refitting seemed a pointless task if it was only to leak again and a new tank was only £100.


Once the tank was refitted the leak disapeared and all appreared well. I met up last week with one of the club members and when we came to leave the car wouldnt start. It has done this a couple of times before but after leaving for 5 mins it would start.


On this occasion it didnt. Rob suggested I took the fuel cap off to see if it had created a air lock. This resulted in me being showered with literally half a gallon of tescos finest momentem petrol!!! The tank had done 150 mile and was on 1/4 of a tank.


Car still wouldnt start for another 2 hours. in fact putting a tow rope on the front towing eye was enough to make it start and I drove half a mile home.


The drive home was enough for the tank to build pressure. Ive since removed the gravity valve which appears in good order but only operates 1 way to let air in the tank but not out? If i blew air in the valve it only allowed it to pass 1 way irrespective of orientation. When not level it wouldnt let air pass in either direction. I then reversed the valve so it relieves pressure from the tank. The valve is marked which way it should go and was correct but i reversed it.


The tank is now breathing and I thought all good. Ive just filled up with fuel despite struggling to fill up as now the tank wont allow air in and the petrol pump kept tripping out.


When it was full it gushed petrol out of the filler neck.. I drove home and the petrol is now siphoning out of the tank through the trumpet via the gravity valve???


So my question if people havent fallen asleep is should the valve be 2 way and mine is knackered?


Im looking to get a replacement but cant find one so far?


Also should i just blank it out and try not to roll the car

I'm pretty sure you should be able to blow through the gravity valve both ways when it's the right way up, as it is a pressure vent and also draws air in to replace used fuel, but someone else may correct me. Then obviously like you say,  it shuts off when upside-down to stop fuel going everywhere in the event of ending upon your roof or something.

I need to check my gravity valve, as mine does what you have described (it leaks fuel out of the trumpet) but mine only seems to do it when it's really hot weather, the tank is near full and when the car is just switched off.

Got a fair rush of air when took filler cap off too yesterday when tank was practically empty

I've also tried looking for a replacement to no avail, and I'm unsure as to whether they can be effectively cleaned out as surely it is just a ball valve really?

As for removing it and trying not to roll the car,  it's not a route I'd personally take as it would always be in the back of my mind

Did a bit of research quickly as I doubted myself,  top outlet goes to trumpet breather and you should be able to blow through it quite freely, the bottom to tank should be more resistance blowing through it but should be able to if you blow hard enough.

Had similar confusion over one of these and got help on here. Make sure you have it the right way up when blowing through it otherwise it simply passes air.

I used to get the rush of air from my tank. Replaced the tank and all breather pipes. New accumulator and pump and now it does not do it.

Recent hot weather a good smell of petrol near the car so assume
Breather was working overtime. Back to normal now.


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I've got a new tank and all that too,  I've read that a rush of air is a good sign, so long as its not too excessive?

I will check gravity valve again when I get a chance but given I get no issues other than near full tank in hot weather I might just put it down to breather working overtime for now too. Don't suppose it should be venting fuel though

When the valve is in its correct orientation, it works both ways.  I think its there to allow the tank pressure to equalise, but to stop it daffodil fuel out when the car is on its roof (fire risk, apparently).

Easy to check, just pull the inner arch off and give it a rattle, it should feel like a golf ball in an egg cup.

The bracket that holds this to the inner wing rusts through and fails, so it might have fallen into a position that blocks it.

Also, whilst you're there, check all 4 pipes into the tank are free flowing, there have been replacement tanks with welding debris left in the pipes from manufacturer.  

How big is your egg cup?  Ostrich eggs for breakfast I guess


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Thanks for the comprehensive replies everyone. Well I've taken the valve off again and filled it with cleaner and then compressed air to blow it out and it now seems to pass both ways when in correct orientation. I've refitted to the car and so far so good and no pressure in tank. 

I've now got a couple of weeks holiday so will see how it is when I return. Thanks everyone !