Probably as it's not designed as a lock
It's a anti misfuel device it's only supposed to open for the correct sized nozzle
Or at least that's what I thought it was
It was designed as an anti-misfuel device.
Unleaded fuel nozzles should be a smaller diameter than diesel ones. There are in fact two diesel sizes, but you only find the bigger ones at truck only filling points, as this allows a faster flow for their enormous tanks. £1000 or more to fill up?
The smaller nozzles were introduced with unleaded fuel, to prevent using leaded, which would destroy a catalytic converter. Until then, all nozzles were the same size.
I think it was Ford that invented the flap, and announced as a wonderful idea to prevent misfuelling. In reality, I think only the diesel vehicles benefit, preventing the unleaded nozzle from opening the flap, but the larger diameter diesel nozzle won't fit into a petrol car, so no need for anything fancy.
When petrol stations would replace their own nozzles, it was not rare to find they'd used a large one for petrol or a small one for diesel, but with so few small stations around, that is less of a problem. The larger stations all have professional pump engineers do any servicing or repairs to pump, hoses or nozzles. (I've replaced a few hoses and nozzles, between 1972-75)
The smart fuelling system does avoid the loss of fuel caps though.
