Fuel tank ventilation Series 3 double six 1979
 

Hello,
I accidentally ran out of fuel and when I opened the cap to replenisch I heart a sissing noise (sucking air) and the metal tank itself made a short noise as if it expanded due to the dissapering vacuum in it. I wonder if a fule tank shoundn't be ventilated?

There is a vented line as these tanks are prone to collapse by vacuum. Check all your hoses to the tank from the filler to the evap system.

Venting applies to any fuel tank with a sealing cap.


Originaly in recent vehicle history, vented to the atmosphere.


Then, a transition. Fuel caps came vented and unvented. Unvented caps on a non vented tanks caused issues or at least consternation.


In areas where emission laws are strict, complex venting is installed. Objective, direct the fumes to the engine to burn.


Jaguars have pipes from the top of the tank, up the C posts, dowen again and thence to the right front wheel well. A canister and one way valve are found there. The canister is packed with charcoal. in turn, it is relieved of vapor by a pipe to the intake manifold.


Failures can occur in two ways anywhere along the way. Rust through, vapor to the atmosphere. usually un noticed.


Plugged or filed one way valve. As fuel is withdrawn from the tand, a vacuum begins to form. when the pump can no longer over come the vacuum, the engine stops running...


A whoosh on opening a tank is air rushing in to the vacuum. Old rule in physics. Nature abhors a vacuum....


Carl

Many thanks to all!

Does someone knwos if on eurropean cars like that one (XJ12/double six pre HE 1979 Series III ) there is also a EVAP system?

Hello, How can one debug that? Are there things one could start with.
Is there a way to exclude the tank beiing under pressure instead of vacuum, since I guess it ll make the same noise?
It's a European car, not the strict emissions as in USA. Do all XJ12' have charcoal canisters? Where are those located? Where is it gooing to (to be burned?).

Just a surmise.


L:ook under the right front wing. Is there a canister there? If so, it is a part of a captive vapour recovery/tank vent system.


If absent, it is an open system and intended to vent to the atmosphere. Check the upper throats of the filler. A small hole. Free and cleat or clogged in whole or part?


Carl.

Thanks for info, I'll have to stop the debugging proces for a few months, but afterward i'll post again!