Petrol Cap Seal

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myoldjalopy
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Petrol Cap Seal

Postby myoldjalopy » Wed Jun 26, 2019 4:01 pm

Petrol has been seeping out from my petrol cap when going up steep hills with a full tank. I have ordered a new cork seal and intend to glue it in place with impact adhesive. Will that be OK - or should I do anything else to make sure it stays in place and creates a good seal?

ManyMinors
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Re: Petrol Cap Seal

Postby ManyMinors » Wed Jun 26, 2019 4:17 pm

I really can't see any adhesive being much good I'm afraid. For what they cost, I would just order a replacement cap. A missing seal makes a car unroadworthy and is an MOT fail point.

philthehill
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Re: Petrol Cap Seal

Postby philthehill » Wed Jun 26, 2019 5:04 pm

As the cap is vented petrol will come out of the filler cap when going up a steep hill if the tank is overfilled and even if the seal is new.

If the cap was not vented the fuel pump would not be able to pump petrol and if it was able pump petrol the vacuum created in the tank may even collapse the tank.

The answer is not to fill the tank right to the brim.

As regards the MOT - my motorcycle has a seal on the cap but it also has an original factory fitted vent in the cap which is connected to an open pipe which originally vented down through the headstock.

The filler cap seal is always checked at the MOT but the exercise is pointless as the cap has the open vent but the box is ticked. 8)


KeithL
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Re: Petrol Cap Seal

Postby KeithL » Thu Jun 27, 2019 11:27 am

When I fill our Traveller I usually stop at the first click if not before. As well as stopping the seepage going uphill it avoids petrol sitting in the filler pipe which, unless it has been replaced recently, is almost certainly not ethanol resistant and will, over time, start to degrade.


myoldjalopy
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Re: Petrol Cap Seal

Postby myoldjalopy » Thu Jun 27, 2019 11:39 am

OK, thank you for your answers. I have only really noticed this problem recently and, like 'KeithL', stop filling once the pump handle clicks, so I don't think I am regularly over-filling the tank.
Therefore, all I think I can do is fit the seal when it arrives and see what happens. The seals must be in the cap for a purpose. A little bit of fuel might seep out from the breather hole, as Phil suggests, but a leaky seal might, perhaps, make it a lot more.

simmitc
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Re: Petrol Cap Seal

Postby simmitc » Thu Jun 27, 2019 12:42 pm

Petrol is a good solvent for many well known impact adhesive products, so such glues are not ideal to fit a seal.

myoldjalopy
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Re: Petrol Cap Seal

Postby myoldjalopy » Fri Jul 19, 2019 9:56 am

To report back - I did use Bostick in the absence of any alternate suggestions and am pleased to say that, so far:
a) it has stopped the fuel leak 8)
b) the seal is still in place - I'll let you all know if there are any problems down the line.
I wonder, did they always use a cork seal? The remains of my old one, which had shrunk up against the inner convex area of the cap, seemed like a kind of fibre material. I know some caps use rubber.........


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