20-02-2021, 11:55 PM
(This post was last modified: 20-02-2021, 11:57 PM by Colin Morgan.)
Found this on the Hereford A7 site from 2017:
"Rear fuel tank breather
From August 1934, the low chassis Austin Seven Jewel range were introduced. From the
introduction of these new models, all petrol tanks were in a concealed position at the rear of the car
with a steel filler pipe projecting towards the rear wing. The actual filler pipe was joined to the tank
pipe by a flexible hose which was quite close to the spare-wheel compartment.
Austin realised that any leak from the filler pipe caused by overfilling could result in petrol fumes
entering the car. To prevent this happening, an overflow pipe was fitted to the front of the petrol
tank just behind the back axle. So, if petrol is seen dribbling from underneath the rear of the car
when filling with petrol, you have probably overfilled the tank. This is not an uncommon occurrence
especially as our elderly petrol gauges become less reliable. To prevent this happening, it is possible
to plug-off the overflow pipe either with a tapered hardwood plug or with a central heating
microbore (probably 10 mm) blank-end. (slightly less safe to smoke in the car though …. Ed)
Clearly, it is best to avoid over-filling ……. Eddie Loader"
Also, there was a discussion on the previous version of this site, many years ago, concerning the expansion of petrol after filling up from a cold underground tank - with the possibility of overflow then occurring should a tank be filled to the top. Sandy Croall calculated that expansion might be as much as a pint on a hot day. This could be enough to set the overflow syphon effect off? However, if the the overflow is blocked, then any expansion would occur (relatively - assuming no leak) harmlessly up the filler tube, with air escaping from the unsealed filler cap?
"Rear fuel tank breather
From August 1934, the low chassis Austin Seven Jewel range were introduced. From the
introduction of these new models, all petrol tanks were in a concealed position at the rear of the car
with a steel filler pipe projecting towards the rear wing. The actual filler pipe was joined to the tank
pipe by a flexible hose which was quite close to the spare-wheel compartment.
Austin realised that any leak from the filler pipe caused by overfilling could result in petrol fumes
entering the car. To prevent this happening, an overflow pipe was fitted to the front of the petrol
tank just behind the back axle. So, if petrol is seen dribbling from underneath the rear of the car
when filling with petrol, you have probably overfilled the tank. This is not an uncommon occurrence
especially as our elderly petrol gauges become less reliable. To prevent this happening, it is possible
to plug-off the overflow pipe either with a tapered hardwood plug or with a central heating
microbore (probably 10 mm) blank-end. (slightly less safe to smoke in the car though …. Ed)
Clearly, it is best to avoid over-filling ……. Eddie Loader"
Also, there was a discussion on the previous version of this site, many years ago, concerning the expansion of petrol after filling up from a cold underground tank - with the possibility of overflow then occurring should a tank be filled to the top. Sandy Croall calculated that expansion might be as much as a pint on a hot day. This could be enough to set the overflow syphon effect off? However, if the the overflow is blocked, then any expansion would occur (relatively - assuming no leak) harmlessly up the filler tube, with air escaping from the unsealed filler cap?