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Fuel tank vacuum


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As the sun has made an appearance I decided to take my wife to garden centre today, what could go wrong, no room for her to buy much :) . We got there fine, 26 miles and the car ran great, on the way back however I took a sharp LH bend at speed and the car started hunting for fuel, tank was at less than 1/4 and I'd read this could be an issue, anyway I carried on and all was well until the last 6 miles or so, the car wouldn't accelerate much, if I kept it at around 50 it was ok but something wasn't right, fuel level now down around 1/8 so I headed for nearest petrol station. When I opened the filler cap, there was a lot of pressure in the tank, more than I've experience in any other car, my question is, should there be a breather somewhere? I filled the car and it drove home fine.

Edited by iani
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Just fitted a round, locking, cap and so far, so good. The cap that was on it was an original style one, no sign of any breather hole though.

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Whilst I would always bow to Stuart's knowledge on these things, I have to say that mine doesn't have a breather in the cap either, as it vents through a hole in the neck. I think this may be a US version.

 

Anyhow, if yours is like mine and the rubber collar linking the neck to the tank is covering the hole, it won't be able to breath.

 

Worth a look.

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The cap should have a breather hole, you may have the wrong one fitted.

Stuart.

+1 The rubber seal should have a hole in the centre about .100" in dia, There were about 5 years ago ones, being sold by the usual suspects with no vent hole? You need to check that! at the time, I did point this out to the Sunbury boys.

 

Bruce.

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The US Style magnetic cap has a rubber seal under the cap and a breather hole in the side of the neck that goes via a tube to the expansion tank on the side of the boot and that should then be piped forward to the charcoal canister. It can be used without but you would still need it to vent externally via a pipe to atmosphere.. The UK style one does vent through the sprung loaded plate under the cap but as the fibre "O" ring in the top of the neck is quite often worn away then venting occurs quite easily round there too!

Stuart.

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Hi Stuart,

You amaze me (and probably others) with your deep knowledge, again.

Best regards,

Waldi

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No problems today and it's hotter, the new cap must be venting correctly, the previous one issue obviously fairly new.

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The US Style magnetic cap has a rubber seal under the cap and a breather hole in the side of the neck that goes via a tube to the expansion tank on the side of the boot and that should then be piped forward to the charcoal canister. It can be used without but you would still need it to vent externally via a pipe to atmosphere.. The UK style one does vent through the sprung loaded plate under the cap but as the fibre "O" ring in the top of the neck is quite often worn away then venting occurs quite easily round there too!

Stuart.

 

Yes, mine is piped to atmosphere through the same hole as the fuel pump overflow. It wasn't when I bought the car and took some tracking down as the source of petrol fumes!!!

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No, my car is a UK CP car, the previous owner had bought a new cap from Rimmers, it has a solid rubber seal when it should have had a hole in the centre, as per their 718738 part number.

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