leaky fuel filler


my rocky when i put more than 3/4 of a tank in leaks out of the fuel filler and fuel runs down the outside of the car.
this comfuses me as the filler cap proper clamps down well, and the filler neck dont leak.
where is this coming from?


Ssome tanks have a small diameter tube to release air pressure. If the tube is blocked your fuel tank might become pressurised and showing the leaks. Look under the car towards the filler neck, below the filler cap, where a small tube might be seen.If there is one has the outlet been blocked by mud? Alternatively is the filler cap worn so fuel leaks when the tank gets pressurised - renew the rubber seal within the cap [make one from an an inner tube] etc.