Mine looked clean too.
No idea if it's significant but replacement one had different coloured parts inside the yellow cap - different manufacturer or a redesign? Who knows! 2011 SD4 HSE Auto
(Previously 2007 TD4 XS Manual)

Interesting. Mine has yellow outer, then white internal casing clipped to a black ring underneath. Spring section inside has a grey plastic bit.

So did my original but on the replacement the grey bit was replaced by a pinkish/purplish bit. 2011 SD4 HSE Auto
(Previously 2007 TD4 XS Manual)

New filler cap fitted (thanks Dan for speedy...) ... went for 30 min drive. Parked up. Removed filler cap. NO wooosh, no vacuum, easy to remove. Problem gone away. ...

Be true to yourself. That way happiness lies...

I am still waiting on mine from Dan

Had the same on my 3.2 petrol. I used a surgical drill to drill through the valve ion the inside of the filler cap
Problem solved obviously a sticky pressure valve - FL2 3.2 i6 - There is no Replacement for Displacement

If my wife ever sells my stuff for what I told her I paid for it, there will be some bargains out there!

I just want to confirm that regardless of whether or not the hissing/vacuum is an issue, the new design filler cap solves the issue. Everyone who has replaced their cap suffers no vacuum now n

Mine fixed completely by replacement cap. 2011 SD4 HSE Auto
(Previously 2007 TD4 XS Manual)

Few weeks on and no hising here either

After stumbling across this topic, it reminded me that I had noticed this vacuum effect on the last few fill-ups, so I took the cap off and checked it over. If you squeeze the outer case to make it oval you can ease one side of the base up and then gently ease out the rest from under the barbs. This allows access to the underside of the valve. I then poked a probe into both sides of the vent and wasn't surprised to find it stuck closed. Although it seemed clean enough, something had made it lock up solid.

I assume the strong spring prevents leaks due to expansion, and the weak spring allows air in to reduce the vacuum caused by the pump. The key technical point is whether the pump is powerful enough to overcome the highest possible vacuum caused by drawing all of the fuel out of a sealed tank. My hunch is that this is going to be well outside of the pump's working range and this almost certainly explains why the cap has a built-in venting valve.

IMO, "They all do that" is rarely an acceptable answer to a technical question relating to any design feature or fault and I am always suspicious of people who seem to be utterly convinced by anecdotes from unqualified sales execs. Asking "why?" usually brings the conversation to an abrupt end.

Any ideas on why it locked as I get this on mine?

Hi Rich. Not sure why it sticks - could be a long term chemical change in the plastics or some kind of fuel residue that slowly bakes onto the seal. I'm wondering if a dab of petroleum jelly or a squirt of silicone might reduce the effect but I would rather know what the materials are before applying anything since it could degrade the seal. In any case, the fuel vapour is likely to wash anything off, so, in the absence of detailed information, I guess a quick poke is the best solution!

Thanks, will take a look.

Hissing noise, do you use Esso? not still got a Tiger In Your Tank by any chance??

Well no tigers but the small spring was stuck as Mando has said. Managed to free mine and it now appears to be working fine, will have to monitor it and when it starts hissing I will have to take it apart again. What's the point in owning a Landrover if you can't take it apart!