Fuel Tank Venting and Overfill Protection

Fuel tank venting and overfill protection





When fuel is added to the tank air is evacuated partially through the breather pipe (3).

An air cushion is formed at the top of the tank when the level of fuel reaches the lower opening of the breather pipe (3), owing to the action of a constriction (5) positioned in the breather hose (4) for the upper section of the tank. The constriction inhibits rapid changes in volume when the car is being refuelled but does not affect gradual changes in volume occasioned by temperature variations or the movement of the car when it is being driven.




The tank is vented externally through the vent hose (6) which runs from the filler pipe up the rear corner pillar and along the roof (above the headlining) down through the left front corner pillar and into the engine bay. On late-production model year 1985 and later cars the vent hose is connected to a spigot on the outer end of the filler pipe.

Under normal conditions, the filler cap makes a tight seal with the filler pipe. However, the cap incorporates a vacuum valve which will prevent the fuel tank from collapsing as a result of the pressure difference that could arise if the ventilation system should become blocked.