Pressurised fuel tank

[Gophur]

Hi guys,

After reading Ross9's fantastic write up on his T4, I noticed his comment about having a problem with a pressurised tank.

Now, I do a lot of mileage in my car and always run the tank from full up to almost completely dry, and when I come to fill it and release the fuel cap there's always air to release, and usually a fair amount too.

Is this something I should worry about? Not really heard of/experienced it before?

[vjck_uk]

are you sure its pressure and not a vacuum? which would suggest the breather is blocked

[Gophur]

I thought that to be honest, but no I'm pretty sure it's escaping rather than inhaling.

Where abouts is the breather pipe on this car?

[DutchV40]

I also have over pressure in the tank.
When hot outside it is really present.
When releasing the fuel cap the pressure comes out. I feel it.
They say that this is normal behaviour...

[Gophur]

Hmmm, this isn't when it's hot though, this is pretty much on every fill.

I'm not hugely worried about it, more curious than anything.

[pyaap]

Personally, I wouldn't worry too much about pressure being released from the tank. The standard system does not have a fuel return line and pressure is maintained via some sort of "accumulator", hence pressure is maintained even when the engine is switched off - this was done by Volvo for "emissions purposes". Having said that, the vapour canister usually works reasonably well to try and minimise this so as has been mentioned, just make sure that none of the valves on the return vapour line to the intake are either blocked or have degraded.

As for Jacq's setup, with a return line, you're returning hot fuel back into the tank and because its a closed setup, the vapour will slowly build up; the stock vapour canister cannot really cope with this (was never designed for that purpose) hence there will be significantly more pressure.

[renaulthater]

Its Normal !!!!!!!

[Gophur]

Cool, alright I'll give it a proper good check over to make sure nothing's obviously moody.

Cheers for the advice!

[PNuT]

assuming its a simular set up too a T5 i would assume your evap system isnt functioning as it should....

i removed my complete system as a new one way valve was going to cost in the region of £50 & blocked the pipe from the tank......

i get loads of tank pressure but it hasnt caused me any problems