Fuel tank vacuum

My 2.5TD is creating a vacuum in the fuel tank when I drive along, after a while you can hear the tank flexing and if I take the fuel cap off after a run a lot of air is sucked in. This was happening when I bought it, I replaced the push in cap with what I believe to be the correct one (STC4072) but it is still happening, is there something I'm missing?

turtle

Hi Michael,

I'd guess that it's not a vacuum but pressurising the tank. I had this happen on mine and used a quick search on here to find the solution. Try "2.5TD Boost Diaphragm".

HTH

Thanks form that I'll give it a go and let you know