Fourtrak fuel tank vacuum


I've got a vacuum developing in the fuel tank which releases with a 'hiss' everytime I open the fuel cap, and occasionally I can hear glugging and air movement noises whilst I'm driving. This is presumably the tank trying to suck some air in when the vacuum gets too much.
I remember ages ago on here somebody saying something about a breather that stops working or gets blocked, but I haven't been able to find anything by searching the site.
Can anybody tell me what is the most likely cause of this and how to put it right please?
Very grateful for any advice.

Tank breather


I also remenber a post about this problem, it seems there is a ball valve/spring assembly attached to the neck of the fuel filler which can seize up.

Take a look at the fuel neck filler on 'Milners' site (top of page 'Parts Dealers') it seems to have a small bore pipe coming off the main filler neck, this could be where the valve is situated.

I have heard folk tales of tanks collapsing due to the vacuum, may have been plastic tanks.

Edward (ews) '92 Fourtrak 2.8 TDX

quick fix is to drill a

quick fix is to drill a small hole through the filler cap. ive done it in the past on road cars, dont know if the mot man would witter about vapour emmissions now though, or if it would leak rolling arround offroad.

Close to the filler opening

Close to the filler opening is a pipe that comes off the main one. I think that's the breather. I unplugged the rubber hose from mine and pushed some strimmer wire through the hose back to the tank. I don't know if this is right but it worked for me. Good luck.

Tank Breather

Yes there was an article as i posted it; basically the fuel tank has three small pipes on the offside of the vehicle, one of these has the breather unit fitted to it. This is a small plastic body which contains a small ball bearing and two springs, the two springs locate the ball centrally in the unit, when vacuum is applied it moves the ball one way. When pressure is applied it forces the ball the other way.

As this is located under the vehicle in most variants, it has a propensith to become blocked over time, or simply corrode internally. If it is corroded it can usually be cleaned by spraying a cleaner/lubricant into it, and pressurising it in each direction until it is free, then lubricate it fully by immersing it in light oil.

Thanks for all the advice

Thanks for all the advice guys. Sounds easy enough so I will add it to the list of other jobs to be done as soon as lambing finishes and the weather warms up a bit. Brrrr!
Other jobs planned are:

Front and rear anti roll bar bushes,
Complete new exhaust,
Front brake pads and brake fluid change,
Oil change service including air and fuel filters,
Fan belt and PAS belt change,
Timing belt change (this is the only one that's bothering me. Any advice for a simple and trouble free change would be greatly appreciated!)

That little lot should keep me busy for a while. Biggrin