Editors Note: The original gas cap on 63-70 Avantis were NON-VENTED. The tank vent/overflow is a hose running from the top of the tank to the passenger side of the car and dumping over the outer portion of the axle. The vent hose loops up into the passenger side body sail ( rear portion of the roof behind the quarter window ) in order to maintain the same level as the filler tube on the drivers side.

Filling the tank and topping it off will result in a fuel spill over the axle. The amount of fuel held in the filler tube to the to of the tank could exceed a couple pints at least. IMO, the factory used a non vented cap to prevent fuel from splashing out the vent in a cap and running down the side of the car. The paint in those days was Lacquer and susceptible to damage by the fuel.

May 2010 sdc #41824 1)Laemmie

I have now found that the proper number for the Avanti is a bit of a pain to utilize..............
Stant number 10623 non locking cap is smooth with no outside serrations and is large to get ones fingers to turn it
........Number 10491 is a locking cap and is smaller so no problem with your fingers...........

but for those who do want a non-locking cap I have found that Stant number 10640 is a direct fit
...and it has raised finger grips.....a breeze to put on and take off.

STANT Part # 10640 OE Equivalent Fuel Cap; 2 17/32" Vented Anti-Surge (1 1/2" x 1 3/8" Shallow Cam)
Category: Fuel Tank Cap

The caps are all vented anti-surge. I did some detective work with the Stant site and others...........then called Stant directly to make sure.........good to go.........so if you want a non lockable cap go with 10640 or l0491 if you want the lock. ------------------------------------- The 10623 is a pain to remove since it has no serrations to hold onto. --------------------------------------