Imploding Fuel tank

There should be another breather pipe (separate from fuel filler breather pipe) look at the photo of the new tank and there is another small breather pipe connection, check the pipe from this is not kinked or blocked or if it is not connected and breather connector blanked off.

Scooby22 said:

There should be another breather pipe (separate from fuel filler breather pipe) look at the photo of the new tank and there is another small breather pipe connection, check the pipe from this is not kinked or blocked or if it is not connected and breather connector blanked off.

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There are no additional breathers on the early 110 fuel tanks other than the filler cap, the breather pipe that runs to the top of the filler is primarily to aid filling the tank.
There is a short redundant pipe at the top of the tank (same side as the filler) which should be blocked with a nut.
I'm not sure what this redundant pipe is for, but the tank is also used in old Range Rovers so could be for anything.

marksman said:

Hmm, "Brand new" filler cap ? are you sure it has a breather in the cap (or elsewhere) to equalise the pressure as the fuel is consumed ?

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Haha, no i'm not!
The car has been out of my care for about 2,5 years. It's been at a porsche garage for the last 1,5. They've connected new filler/breather pipes, filler cap and fuel lines in the motor compartment. This to swap out old lines and accommodate for a webasto diesel heater. I'll just re-check everything they've did!

Rougharse Racing said:

It can't be a coincidence that you have fitted a new fuel cap and are now experiencing a vacuum build up in the tank.
From memory the breather is behind the disc held on with two screws inside the cap, however if the new cap is causing problems you may be better using parts of it to repair your old one.
I must say that I am impressed with the vacuum created by the fuel pump!

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Yes, me too! I guess it's safe to say the pump is in good working order!
I'll bring her to the my workshop today and start a full system check. Including cap and breathers!

Scooby22 said:

There should be another breather pipe (separate from fuel filler breather pipe) look at the photo of the new tank and there is another small breather pipe connection, check the pipe from this is not kinked or blocked or if it is not connected and breather connector blanked off.

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There is, but as Rougharse Racing states out, it is blocked. Been thinking of connecting that with a non-return valve to a pipe somewhere around max-wading height. That way i'm sure to have sufficient tank breathing!

Wimblowdriver said:

That would be a dangerous thing to do. The fuel tank is not a pressure vessel. Does it matter that it is dented? - live with it as it is.

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You definitely can use compressed air to reform the tank, but you do not need that much pressure. I had exactly the same problem (after replacing the fuel cap with the non vented version!) and I used a standard foot pump to pressurise the tank and reform it. If you were sticking 10bar in from a compressor it may be an issue, but carefully pressurising it to expand it out is not a problem.

What colour is the fuel filler cap, the vented and non vented version are different colours.

flokkie-b said:

I don't think so, i just had a look under the car again and, as i didn't build it with one, there is no bash plate. That would also mean the drain plug is attached to the bash plate and wouldn't explain the buckling on top of the tank... So, i don't think that's the case.

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There should be a plate under the tank called a cradle, to hold it in place. It is not strictly a bash plate as is only thin and has a hole in it around the drain plug so it can still be accessed. IF is is damaged from impact a proper tank guard will prevent it in future, but I am going to side with everyone els eon the thread and say it looks far more like it is creating a vacuum from a blocked (or non existent if the wrong cap fitted) breather.

dag019 said:

You definitely can use compressed air to reform the tank, but you do not need that much pressure. I had exactly the same problem (after replacing the fuel cap with the non vented version!) and I used a standard foot pump to pressurise the tank and reform it. If you were sticking 10bar in from a compressor it may be an issue, but carefully pressurising it to expand it out is not a problem.

What colour is the fuel filler cap, the vented and non vented version are different colours.

There should be a plate under the tank called a cradle, to hold it in place. It is not strictly a bash plate as is only thin and has a hole in it around the drain plug so it can still be accessed. IF is is damaged from impact a proper tank guard will prevent it in future, but I am going to side with everyone els eon the thread and say it looks far more like it is creating a vacuum from a blocked (or non existent if the wrong cap fitted) breather.

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Thanks for the input dag!
The fuel cap is just a standard black version, don't know what that means for venting....

I finally got the landy back to my workshop yesterday, so i'll start working it today. I'll pressure test the filler cap to check the vent. Furthermore, i'll try to bend the tank back by slowly increasing the pressure in it. Foot pump might not be such a bad idea!

flokkie-b said:

Thanks for the input dag!
The fuel cap is just a standard black version, don't know what that means for venting....

I finally got the landy back to my workshop yesterday, so i'll start working it today. I'll pressure test the filler cap to check the vent. Furthermore, i'll try to bend the tank back by slowly increasing the pressure in it. Foot pump might not be such a bad idea!

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When I did mine removed the vent pipe from the filler neck and jubilee clipped a cut off bicycle inner tube valve into the pipe and then used a foot pump. It did not take much to then pop the tank back to a more normal shape (will never be perfect again). The black caps I think are the vented cap, so I would guess the vent is blocked, think the non vented ones are grey from memory.

You need to go old school and stick a rag in the pipe.

Done and fixed! I just combined the bits of advice of dag019 and mick the builder.
Put the hose of my tire inflator pistol in the pipe and closed it with a rag, then gradually built up the pressure and within seconds the tank came back to its original form!

The took apart the new filler cap and the old one (completely busted because of lost keys). From the outside, the two caps look identical, identical black housing, identical backplate. But on the inside, there were some differences! And yes, the new cap was completely closed of. The old one did have a venting valve behind the backplate.

So, two little holes drilled through the inside of the cap, behind the backplate and we're venting again!

Thank for all the advice!