i was wondering why some a body gas tanks (and maybe other models) were vented with the tube running inside the trunk along the filler tube and some were unvented. is it a simple matter of which gas cap you use or is something else involved? i'm getting ready for paint and want to use the right cap out of my selection. thanks, dave

All tanks have to be vented. The methods however vary. It could be a metal tube or a vented gas cap. Your FSM should help you out.

It might have something to do with wether the car has interior access to the trunk area, a fold down rear seat back. 67-69 Barracuda FB's have a vent tube and fold down rear seat back. My 75 and 76 Dart Sports had no vent tube and did not have fold down rear seat backs.
I would bet its more of an overflow tube than a vent. Didnt vented caps go away with the onset of tighter emmisions standards?

70to71 had a vent tube in the filler neck 72 to 75 idk about 76 but they had it in the gas cap i think

1970 should have a vent tube in the trunk on California ECS equipped cars only. My 70 dart has it, but 99% of the other 70 darts I have ran across do not. The extra tube in the trunk has rubber lines coming off the gas tank that run up inside the tube. It's more of a vapor catch system I think.

It had to do with the ECS - Evaporative Control System. In other words an ECS tank had four vents (I believe one in each corner) that collected the vapors and then sent it to a charcoal canister that then used engine vacuum to suck the fumes into the intake manifold. . . .

The early 68-70 tanks came WITHOUT a vent tube on the tank - so you would probably have to use a vented gas cap. Also, the early tanks are 18 Gallons US. The later tanks for A bodies, 71 and up were 16 Gallons US.

I had to replace the tank on my 76 Plymouth Feather Duster - I like the idea of additional capacity, ordered the older model tank. No vent tube on the tank - no biggy, the gas cap is vented - if not then can drill a 1/8 inch hole for a vent. The tank fits perfectly - only little hiccup, is the filler neck location is about 1/4 inch towards the front of the car. So the rubber piece that the filler neck goes thru the trunk floor, is pushed 1/4 inch to the front. everything else is fine.

Mark
A12rag

picture of 1971 tank:

Steve that is an ECS type tank with the 4vent tubes out the side

in 71 the 4 lines run to a tank. there is an additional line from that tank to the right(pass)side fender, where it is connected to the valve cover breather. the 70 and earlier tanks vented under car, with 1/4" steel line(IIRC). 72 and up used a different venting system, used for smog control purposes.