Hello everyone. My 1st ever post here having recently bought a Series 5 Aero 8. I found this thread whilst researching my problems filling my car. Thought I'd weigh in with what I found out and what has solved (Well, at least vastly improved) the problem for me.
Fuel filling problems.
First, how a petrol station filler nozzle works.
The petrol station filler nozzle draws a small air pressure vacuum through the tiny hole at the tip of the filler nozzle underneath where the petrol (or diesel) emerges.
Internally, the gun uses this vacuum to activate the fuel flow valve through a diaphragm valve.
If the vacuum is present the valve can open, If there is no vacuum (for instance because the hole cannot draw air in when immersed in fuel or if the nozzle is covered somehow) the diaphragm valve springs shut (with the “click” that we are all too familiar with)
Getting around the problem
What we are searching for is the right combination of flow rate and nozzle position to keep the vaccum hole unobstructed. Lord knows what happens deep inside the filler tube, but there’s often a combination that just works …… It’s just that I’ve yet to discover is on my A8 !
My solution for now.
Part A
I’ve removed the boot floor above the tank and replaced the plastic OEM one way air vent valve on the pipe that goes from the tank back to the filler neck. One the face of it the valve worked, but the differential pressures involved are very small (about 14” head of fuel) so I thought I’d try a “deluxe” valve. The new one is billet aluminium with a steel ball and 8mm dia ports, it seems to operate very smoothly, cost was £18. This seems to have worked pretty well, I don’t seem to have improved fuel flow rate into the tank, but there is now MUCH less blowback.
Part B
I’ve found a very long thin tapered funnel that goes deep down into the filler neck – the filler gun discharges into the funnel from above and the funnel tends to rotate the fuel into a vortex as it goes into the tank. The tip of the funnel now discharges below the vent pipe mentioned above. So far so good, no blowback and a decent fill rate. The problem is that it’s pretty dangerous in terms of exposed fuel, potential for spills and attention from irate petrol station staff. This being the case I’m just filling jerry cans and pouring them in at home for the time being. The other good news is that the funnels are £3 !
Last edited by Pittsartist; 17/08/26 07:57 AM.
