Engine: TDI: - 850TDI fuel tank pressure buildup

Paul850TDI · Jan 17th, 2017, 13:03

On my '96 850TDI just noticed that upon screwing off the fuel cap the fuel tank is under pressure so I can hear the pressure releas when cap is off. Is that normal? Are these fuel caps vented?
Thanks for any help in advance!

doingitsideways · Jan 17th, 2017, 14:08

It'll be under vacuum, as the pump has sucked the fuel out.

The cap doesn't breathe, but there is a breather pipe on the tank that's probably blocked.

I've heard of tanks being distorted out of shape due to blocked breathers.

colwyn · Jan 17th, 2017, 15:57

I used to get a hiss removing the cap on the v70 then fill it to the brim and it coughs the fuel out onto your shoes and says cheers mate but im full now.

I never knew why it done it, it was like throwing 2 quid away each time

surely the tank return line would compensate the pressure

brickman · Jan 17th, 2017, 16:43

Tank return is all dealt with at the filter in the engine bay on the diesels so far as I know. There is a little plastic valve there, could be that at fault.

My diesel fills up easy, never has pressure or vacuum present and doesn't dribble, so something is wrong with yours.

Paul850TDI · Jan 17th, 2017, 17:22

Quote:

Originally Posted by brickman

Tank return is all dealt with at the filter in the engine bay on the diesels so far as I know. There is a little plastic valve there, could be that at fault.

My diesel fills up easy, never has pressure or vacuum present and doesn't dribble, so something is wrong with yours.

Thank you guys for the help!
Could you explain where is that valve exactly? A picture of it would be even better.

Jan 17th, 2017, 13:03	#1
Paul850TDI Junior Member Last Online: Jan 27th, 2020 20:05 Join Date: Sep 2014 Location: Budapest	850TDI fuel tank pressure buildup On my '96 850TDI just noticed that upon screwing off the fuel cap the fuel tank is under pressure so I can hear the pressure releas when cap is off. Is that normal? Are these fuel caps vented? Thanks for any help in advance!

Jan 17th, 2017, 14:08	#2
doingitsideways The Daddy Last Online: Feb 29th, 2024 15:07 Join Date: May 2010 Location: Manchester	It'll be under vacuum, as the pump has sucked the fuel out. The cap doesn't breathe, but there is a breather pipe on the tank that's probably blocked. I've heard of tanks being distorted out of shape due to blocked breathers. __________________ XC90 V8 Exec, C70 2.4T Convertible, S70 T5 CD, 850 TDI, 2 x Escort vans and a 2.8i Capri. Clearout has begun, but must continue!

Jan 17th, 2017, 16:43	#4
brickman Premier Member Last Online: Nov 14th, 2023 10:40 Join Date: Jul 2013 Location: Glasgow	Tank return is all dealt with at the filter in the engine bay on the diesels so far as I know. There is a little plastic valve there, could be that at fault. My diesel fills up easy, never has pressure or vacuum present and doesn't dribble, so something is wrong with yours. __________________

Thread Tools
Show Printable Version Email this Page
Display Modes
Linear Mode Switch to Hybrid Mode Switch to Threaded Mode

Jan 17th, 2017, 15:57	#3
colwyn Resident Ejit Last Online: Feb 19th, 2024 09:05 Join Date: Dec 2014 Location: Skelmersdale	I used to get a hiss removing the cap on the v70 then fill it to the brim and it coughs the fuel out onto your shoes and says cheers mate but im full now. I never knew why it done it, it was like throwing 2 quid away each time surely the tank return line would compensate the pressure

Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)