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Filler pipe seal to tank
Slimy38 - 29/1/26 at 07:59 AM

I'm having some trouble with my filler pipe, it was just a bit 'pongy' before but now it's just a full on tidal wave whenever I fill the tank up to the top. The tank is a self-built one with a 2 inch pipe on the exit, about an inch long. I'm trying to use CBS's flexible fuel filler from here https://www.carbuilder.com/products/ultra-flexible-fuel-filler-hose-51mm, but I cannot get it to seal on the pipe.

First attempt was a jubilee clip, that didn't seem to help. Next attempt was with a spiral wire clip, that didn't fare much better. At the moment there's one of each and I still can't get the required amount of fuel to stay put.

I was thinking of some sealant or similar between the filler pipe and the tank pipe but I don't know what. I toyed with the idea of PTFE tape, a quick check online suggests I'll just end up with PTFE fibres clogging up my filter and the rest of the system. My brother in law has suggested a section of bike inner tube rubber over the pipe first, again I'm at the whim of the corrosive substance we call 'petrol' nowadays.

Is there a knack or technique I'm missing that would seal the pipe to the tank? It's definitely the seal between the two, fuel is now visible as I fill it up. To be honest I'd have preferred it if it was a failed weld, at least I can fix those.

Frustratingly my 'non-IVA compliant' filler pipe was perfectly fine, stupid me swapped it for the CBS version and disposed of the old one because I didn't think I'd need it anymore. Neither of them had marks, I have an IVA declaration from CBS to say theirs is compliant.

Slimy38 - 29/1/26 at 08:24 AM

I should add the pipe is a snug fit, not so tight that it needs soapy water to fit (like a fuel line), but snug enough that I have to make sure things are perfectly round and aligned before it will slide on.

Sanzomat - 29/1/26 at 09:05 AM

That is odd. From what you've written I can't think of any reason why the pipe you are using should leak with either of the hose clamp options or indeed without a clamp at all as there is no pressure.

Is it possible that there is actually a leak where the metal pipe spigot joins the main tank? As it is only 1" long I'm guessing the hose goes right down to the tank so the leak would be visible in the same place whichever?

I know you say it didn't leak before with the non IVA compliant pipe but its possible the act of removing that pipe and installing the new one could have stressed the metal to metal connection and made a leak there?

Slimy38 - 29/1/26 at 09:21 AM

quote:
Originally posted by Sanzomat
That is odd. From what you've written I can't think of any reason why the pipe you are using should leak with either of the hose clamp options or indeed without a clamp at all as there is no pressure.

Is it possible that there is actually a leak where the metal pipe spigot joins the main tank? As it is only 1" long I'm guessing the hose goes right down to the tank so the leak would be visible in the same place whichever?

I know you say it didn't leak before with the non IVA compliant pipe but its possible the act of removing that pipe and installing the new one could have stressed the metal to metal connection and made a leak there?


Yeah the hose butts right up to the wall of the tank so what you say makes sense, I really shouldn't discount a metal seam leak. I'm going to try and mount the pipe away from the wall with maybe half inch gap, just to confirm which side it comes from.

The problem is the pipe is on the side of the tank rather than the top, so when the tank is full I have static fuel in the pipe. I had to come in on the side due to where my filler cap is on the car (that can't be moved).

Sanzomat - 29/1/26 at 02:06 PM

I believe you need to present the vehicle at IVA with a full tank so definitely needs fixing!

Slimy38 - 29/1/26 at 02:43 PM

quote:
Originally posted by Sanzomat
I believe you need to present the vehicle at IVA with a full tank so definitely needs fixing!


Yep, that's what drove me to this point in the first place, I've been adding five litres every so often until the tank shows full. It would be so much easier if it could be presented with half a tank, but I understand why they do it. It's to highlight issues like this.

obfripper - 29/1/26 at 11:08 PM

The seam in that pipe is going to be pretty suceptible to fuel wicking through it, as I don't think it looks compressible enough to close off the seam completely with just a plain clip.

You're either looking at using a compatible non setting sealer to bridge the gap left when the clip is tightened, or a curing polysulphide based sealant suitable for continous contact with fuel if the remaining gap is too large for a non setting sealer to work.

Something like Wellseal for a non setting sealer, for a curing type something like a small amount of slosh tank leak sealer could be used, polysulphide sealants are a bit specialist and difficult to find in small quantities.

I have used sikaflex 221 pu in contact with fuel in a pinch, but it goes somewhat soft/mushy where in contact with fuel and hardens/dries out on external facing areas, so probably not suitable for your purposes.

My only other thought is in the vein of your BIL suggestion, but place a thicker rubber band (like a coolant hose section) over both the pipes as assembled and use the pressure of a jubilee clip (or for more pressure a mikalor type hose clamp) to create enough pressure to compress the area around the wire tighter (as it will mould around the uneven shape), with the rubber on the outside it is not exposed to any fuel so shouldn't be a problem for iva.

Dave

Slimy38 - 30/1/26 at 07:55 AM

So a quick update.... it's sealed! I reckon it was the spiral wire causing the issue, because I noticed the spiral is in an outer tube with the inner tube being a separate layer. I carefully removed the spiral wire from the first half inch, then clamped on that. I kept a second clamp securing the spiral wire for a mechanical fixing.

The only problem is that in my enthusiasm for removing the leak I managed to overfill it (I filled right up to the cap when it was cold), so I came to a leaking petrol cap this morning. I've cleaned it up and drained off around half a litre, I suspect I might need to do it again as the day warms up. At least the cap is venting correctly.

I guess a follow up question, when they say 'full tank for IVA' are they still ok with filling up to the equivalent of a pump click? IE 6 inches below the cap?

[Edited on 30/1/26 by Slimy38]

gremlin1234 - 30/1/26 at 10:46 AM

could you seal the end of the tube to the tank pipe with self-amalgamating tape?

https://race-tapes.co.uk/electrical-tape/119-scapa-2501-pib-self-amalgamating-tape-25mm-x-10m-black.html

or better (since it mentions petrol)
https://www.sealantsandtoolsdirect.co.uk/everbuild-silweld-black-incredible-silicone-self-fusing-repair-tape

nick205 - 30/1/26 at 10:52 AM

If you've got it full to the top of the pipe, can you not syphon some out before the IVA?

Modern tin tops have anti-syphon things in their fuel tanks/fillers, but I doubt yours does.

gremlin1234 - 30/1/26 at 11:09 AM

quote:
Originally posted by Slimy38
I guess a follow up question, when they say 'full tank for IVA' are they still ok with filling up to the equivalent of a pump click? IE 6 inches below the cap?

I have looked through the iva manual, and the only references to full fuel tanks that I can find, are actually to determine weight!

Schrodinger - 30/1/26 at 11:46 AM

IIRC when I took my Stylus for IVA they asked if the tank was full and just looked at the fuel guage for reading full. So it realy only needs to be near full.

Slimy38 - 30/1/26 at 01:33 PM

quote:
Originally posted by gremlin1234
could you seal the end of the tube to the tank pipe with self-amalgamating tape?

https://race-tapes.co.uk/electrical-tape/119-scapa-2501-pib-self-amalgamating-tape-25mm-x-10m-black.html

or better (since it mentions petrol)
https://www.sealantsandtoolsdirect.co.uk/everbuild-silweld-black-incredible-silicone-self-fusing-repair-tape


Ooh, now that looks good, thanks! I've ordered some of the everbuild just because it sounds like something that will come in useful even if this tank issue is resolved.

Slimy38 - 30/1/26 at 01:36 PM

quote:
Originally posted by gremlin1234
quote:
Originally posted by Slimy38
I guess a follow up question, when they say 'full tank for IVA' are they still ok with filling up to the equivalent of a pump click? IE 6 inches below the cap?

I have looked through the iva manual, and the only references to full fuel tanks that I can find, are actually to determine weight!


As far as I know it's not in the manual at all, however it is on my appointment confirmation;

quote:

Note 3. The vehicle, if a passenger car (M1) or light goods vehicle (N1), must be presented with fuel tank(s) full of fuel unless the vehicle is a standard (unmodified) mass produced vehicle.


But now I read it, it talks about the fuel tank being full of fuel, not necessarily the filler pipe.

Slimy38 - 30/1/26 at 01:38 PM

quote:
Originally posted by Schrodinger
IIRC when I took my Stylus for IVA they asked if the tank was full and just looked at the fuel guage for reading full. So it realy only needs to be near full.


Ah that's fair, thanks. I don't have a fuel gauge but I got it in my head that they will want to see fuel through the filler cap. Then again, that's not possible on tin tops so I seem to be going a bit too far.