It is indeed. I will hopefully report back with good news.

New cap fitted today, different coloured inside caping

As there seems to be a variety of different caps/colours a photo of your new one would be interesting and perhaps a report in a few days on the hissing noise on cap removal.
Cheers

Looking for a Mantec sump guard and tank guard for Fl2 2014. Any one can give a helping hand?

Funky.

I should add mine hasn't arrived yet. Will post as soon as it does.

stevep999 wrote:

Click image to enlarge

Fitted yesterday, opened today.........no hiss. Will monitor

I hope those are the ones Duckworths have!

Received mine today. Same as those above so clearly that's the new (and modified?) version.

Will post results once the car is back from MOT and has had a run.

I can confirm that after a 40 mile drive and the new cap fitted, it still sucked in a lot of air upon opening 😓

Don't know what to suggest
Replacement cap fixed mine. 2011 SD4 HSE Auto
(Previously 2007 TD4 XS Manual)

I'm really disappointed to be honest. Really cant be doing with worrying that there might be an underlying issue. Will get it checked when it is serviced next month I guess.

If you've still got the old cap, how about drilling a small hole in it to use as a temporary measure? I suppose there's a non-zero probability the new cap has the same problem but you'd have to be really unlucky! 2011 SD4 HSE Auto
(Previously 2007 TD4 XS Manual)

As we have two FL2s that do this I had a good look at one of ours and it's basically a pressure/vacuum release valve. I made up a little rig with various diameter tubing and insulation tape and found that if you suck hard enough it will "pop" and let air in. Unfortunately I don't have a vacuum gauge so I don't know how hard I was sucking. However the effective area of the cap is 2.4 sq ins (just measured it) I suppose that if the pressure in the tank was just a couple of psi down then it will take a force of 5lbs to remove it.

One strange thing though, yesterday I parked the car and took the cap off and got the hissing noise as the air entered the tank. This morning I removed the cap again (and the car hasn't moved or been started) and got the same effect. The local air pressure is virtually constant from my barometer so that only leaves temperature to explain a pressure change.

Sorry if this seems a bit nerdy but I was once a scientist.