406 fuel tank breather pipes

[Mike406]

Hi

my 406 often smells of petrol and one of the breather pipes was damp with petrol

tank wasn't full and it had been several days since fuel was added

any ideas

Mike

[Roger Morrall]

Yes, lots

1) you need to do something about this. The fuel tank is effectively in the cabin.

2) it could be the breather tubes, it could be the tank, it could be connections to the tank ie to the filler cap and to the engine, it could be (rather less likely) the fuel gauge or the reserve unit (I’m presuming the 406 has this)

The following suggestions rely on Bristols conservatism, my experience is with a 410

3) to investigate I’d recommend first removing both front and rear seats to give you room to manoeuvre.

4) behind the rear seat backrest you’ll find a flat panel, possibly covered with some, by now very tatty, sound insulation. Remove this panel (the later cars used self tap screws, I’m not sure about the 406) to expose the fuel tank.

5) with luck you’ll find no obvious leaks to the tank itself but you won’t be able to get to look at much of it unless you take it out

6) If you’re happy that the tank is ok I’d recommend checking the outlet to the carb, which on a 410 is taken from the top of the tank via the reserve unit, check it’s gasket as well. Ditto check the gasket on the fuel gauge sender

7) I’d also recommend changing out all the breather pipes as well as the filler pipe as a matter of course, even if they look ok

8) If you decide that the tank has got to come out first get underneath the car, find the drain plug and empty it. It’s heavy enough as it is. Then it’s a case of getting back in the car, undoing and removing the very obvious straps that hold it place, and wrestling it out of the car. It’s heavy and awkward and very possibly well stuck down and you’ll be damn glad you took the front seats out. A friend might be very handy!

9) If there are leaks send it away to specialists to be fixed, (I was very strongly recommended by none other than Brian Marelli NOT to go down the diy route with any of the tank sealants you might perhaps be tempted to buy and mess about with)

10) I forget which specialist Brian recommended me to but these people appear to have the right credentials.

https://radiator-repair.co.uk/repair...op/fuel-tanks/

Hope this is some help

[Mike406]

Hi

thanks for the info

I have had the tank out and there are no leaks from the main body of it

the question is more about the two rubber pipes which go down the underside of the wheel arch and then protrude out under the rear wing

it's one of those that has a damp fuel smell at the bottom of the pipe

I understand what the over flow pipe does from the fuel filler tube, but what does the other pipe do and why would it be wet with petrol

thanks Mike

Originally Posted by Roger Morrall

Yes, lots
Hi
1) you need to do something about this. The fuel tank is effectively in the cabin.

2) it could be the breather tubes, it could be the tank, it could be connections to the tank ie to the filler cap and to the engine, it could be (rather less likely) the fuel gauge or the reserve unit (I’m presuming the 406 has this)

The following suggestions rely on Bristols conservatism, my experience is with a 410

3) to investigate I’d recommend first removing both front and rear seats to give you room to manoeuvre.

4) behind the rear seat backrest you’ll find a flat panel, possibly covered with some, by now very tatty, sound insulation. Remove this panel (the later cars used self tap screws, I’m not sure about the 406) to expose the fuel tank.

5) with luck you’ll find no obvious leaks to the tank itself but you won’t be able to get to look at much of it unless you take it out

6) If you’re happy that the tank is ok I’d recommend checking the outlet to the carb, which on a 410 is taken from the top of the tank via the reserve unit, check it’s gasket as well. Ditto check the gasket on the fuel gauge sender

7) I’d also recommend changing out all the breather pipes as well as the filler pipe as a matter of course, even if they look ok

8) If you decide that the tank has got to come out first get underneath the car, find the drain plug and empty it. It’s heavy enough as it is. Then it’s a case of getting back in the car, undoing and removing the very obvious straps that hold it place, and wrestling it out of the car. It’s heavy and awkward and very possibly well stuck down and you’ll be damn glad you took the front seats out. A friend might be very handy!

9) If there are leaks send it away to specialists to be fixed, (I was very strongly recommended by none other than Brian Marelli NOT to go down the diy route with any of the tank sealants you might perhaps be tempted to buy and mess about with)

10) I forget which specialist Brian recommended me to but these people appear to have the right credentials.

https://radiator-repair.co.uk/repair...op/fuel-tanks/

Hope this is some help

[Roger Morrall]

Hi

From memory, on the 410 one pipe is arranged to catch any splash back from the filler and is connected to the bodywork below the filler cap itself, behind the flap that covers it (as you say) whilst the other is connected to a coil of pipe situated on top of the tank which vents air from the tank, and allows air in as that thirsty engine gobbles the petrol therein. One presumes that the purpose of the coil is to act as a baffle to avoid fuel splashing via the vent.

See Resources on this forum and follow the path to 8 cyl Bristol Cars, then go to 410, then on to page two and then pick up the section on the fuel tank.

I’d expect your second tube to be connected to a similar arrangement.

But this begs the question - wasn’t this obvious when you took the tank out? I presume not, but from memory I’d expect that tube to be routed up from its exit behind the rear side rear wheel through the space between the rear wing and the side of the boot (which can be accessed if you take the side of the boot out) and thence through the bulkhead into the space beside the tank and then up beside the side of the tank to some sort of vent on the tank.

Perhaps this is a case of "incompetent previous owner or mechanic" and the vent from the tank has merely been left to vent into the car and a chunk taken out of the tube. Which could explain the smell of petrol

But that leaves the question as to why that tube should be wet with petrol . I don’t know except to say that I have noticed that petrol sometimes hangs about old rubber for ages.

I hope some of the above might be helpful

If all else fails shove a bit of wire up it and see where it comes out?

[Mike406]

thanks very helpful

Cheers Mike

Originally Posted by Roger Morrall

Hi

From memory, on the 410 one pipe is arranged to catch any splash back from the filler and is connected to the bodywork below the filler cap itself, behind the flap that covers it (as you say) whilst the other is connected to a coil of pipe situated on top of the tank which vents air from the tank, and allows air in as that thirsty engine gobbles the petrol therein. One presumes that the purpose of the coil is to act as a baffle to avoid fuel splashing via the vent.

See Resources on this forum and follow the path to 8 cyl Bristol Cars, then go to 410, then on to page two and then pick up the section on the fuel tank.

I’d expect your second tube to be connected to a similar arrangement.

But this begs the question - wasn’t this obvious when you took the tank out? I presume not, but from memory I’d expect that tube to be routed up from its exit behind the rear side rear wheel through the space between the rear wing and the side of the boot (which can be accessed if you take the side of the boot out) and thence through the bulkhead into the space beside the tank and then up beside the side of the tank to some sort of vent on the tank.

Perhaps this is a case of "incompetent previous owner or mechanic" and the vent from the tank has merely been left to vent into the car and a chunk taken out of the tube. Which could explain the smell of petrol

But that leaves the question as to why that tube should be wet with petrol . I don’t know except to say that I have noticed that petrol sometimes hangs about old rubber for ages.

I hope some of the above might be helpful

If all else fails shove a bit of wire up it and see where it comes out?

[AndrewA]

For what it's worth on my 410, it turned out to be a through bulkhead fitting that was weeping slightly and causing the pong. By that time sender had new gasket and all overflow/breather pipes replaced.

[Mike406]

ok thanks

I sussed that my problem was that the pipe from the over flow was where the smell was coming from

Originally Posted by AndrewA

For what it's worth on my 410, it turned out to be a through bulkhead fitting that was weeping slightly and causing the pong. By that time sender had new gasket and all overflow/breather pipes replaced.