Filler Caps

JohnWilliams6437 · Posted: Tue Sep 05, 2023 4:40 pm Post subject: Filler Caps

Having trouble with my Autovac and one of the points to be checked is 'Make sure the air hole in the Filler Cap is Clear'
Don't have a hole and it hasn't troubled the car to date but as my filler cap is fairly new wondered if it was an original drilling.
Nerdy question - size and position?
I think the Autovac problem is to do with leaving fuel in the tank over a long time (although I added that preserver stuff !)

Nicholas Simons · Posted: Wed Sep 06, 2023 8:15 am Post subject:

Check the two sealing washers at the top as they may have dried out and begun to leak. The slightest leak here will prevent the Autovac sucking fuel through.

JohnWilliams6437 · Posted: Wed Sep 06, 2023 5:55 pm Post subject:

Must be a different type Nicholas- mine has two elbows held tightly into tapered seats,
Discovered a poor soldered joint on the pipe from the filter.
Thanks for your reply.
JW

John Murch · Posted: Thu Sep 07, 2023 6:04 am Post subject:

Any leak on the supply side will cause problems, a poor soldered joint may well open and close with chassis flex. I have experience that problem.
I suspect Nicholas may be referring to the gasket between the tank and top of the unit which has the various valves and pipes attached.
Hopefully you are now all fixed.
As for a hole in the filler, the 3ltr style auto vac doesn't have a screw on filler, so I assume your car is a 4 1/2 I'm surprised that they would rely on a hole in the cap, but no reason why not!

Nicholas Simons · Posted: Thu Sep 07, 2023 8:07 am Post subject:

Yes John, I was referring to the two large diameter cork gaskets that go between the cast metal top of the Autovac, the flange of the inner tank and the main tank.
The filler cap on my ( possibly original ) 3 litre petrol tank has no breather hole. The brass threaded spigot that is affixed to the tank has a narrow slot milled into the thread to provide the breather. Some confusion may exist when talking about filler caps, because I have seen some WOs with a side filler on the Autovac lower chamber.

John Murch · Posted: Thu Sep 07, 2023 3:31 pm Post subject:

The autovac on a 4 1/2 has a much larger bottom tank with a screw on filler cap, I assumed that this is what John was referring to.
The main fuel tank is usually vented as described by Nicholas.

JohnWilliams6437 · Posted: Thu Sep 07, 2023 7:13 pm Post subject:

Thanks for the input John & Nicholas.
I should have made it clear from my first post that i was referring to the Petrol Tank Filler Cap.
As my wife often says 'You only give half the Message' !

Iain Warner · Posted: Sat Sep 09, 2023 6:28 pm Post subject:

The tank filler cap on my 3 litre does not have a hole in it either. As Nicholas says there is a cut out in the threaded boss that the cap screws onto. (Except that mine is soldered up but that is because the car was originally delivered with a pressure feed system)
Iain