Techical Discussions => Tech- - FUEL => Topic started by: Bob Schaefer on June 14, 2010, 08:25:55 AM

Title: Vented Gas Cap
Post by: Bob Schaefer on June 14, 2010, 08:25:55 AM
Ok, so I have been driving modern vehicles for far too long, and I had forgotten what happens when you remove a non-vented gas cap...
So, I was looking on Rock Auto, and they have gas caps for a 1969 Dodge Monaco, and a Polara... and some even say Emission Control, which may or may not mean vented... I don't know. They all, however, say Exc Wagon. Thing is.... That's what I have.
So does anyone know what sort of gas cap I can get that is vented, and will fit my '69 Monaco Wagon?
Alternatively, is there a reason not to get one?
Title: Vented Gas Cap
Post by: Steve on June 14, 2010, 08:51:42 AM
They were none vented caps back then.  If they were vented, the left a trail of gas on the regular body.
Stant has several different options available.  But the way the system is made, you don't want a vented.  Vented would make sense to me too, but it doesn't work
Title: Vented Gas Cap
Post by: Bob Schaefer on June 14, 2010, 09:26:03 AM
That's kinda what I thought... I will go with the big HISS when I remove the cap, and let it work the way it's supposed to...
Thanks again,
Title: Vented Gas Cap
Post by: Guests on June 14, 2010, 09:05:02 PM
Basically before the charcoal canisters and sealed systems, return systems, etc., they simply ran a 1/16th ID steel line from the filler neck, up into the C pillar or somewhere as high as possible, then back down and into the frame rail. It is then near impossible to have fuel come out of the pipe during a rollover, and when they clog/rust up, it takes time to figure out how to fix the problem once discovered.
Title: Vented Gas Cap
Post by: Steve on June 16, 2010, 10:21:03 AM
True. . .But they never released all the pressure, even when new.  Not sure how the wagans are vented. . . I'll look in a manual when i get a chance.
Title: Vented Gas Cap
Post by: Marc on June 16, 2010, 10:29:13 AM
Funny story we got a newer car in that the owner just couldnt figure out what was wrong. Had lost his gas cap and driven with it open for a while, but finaly decided to put an old cap he had lying around on the car. then it wouldnt run right and it would die he changed fuel filter and pump but still couldnt get it to go. turns out it was a non vented cap so my brother got a good running car cheap.
Title: Vented Gas Cap
Post by: sunriee on January 28, 2011, 06:58:50 AM
The vented gas cap is designed to vent small amounts of air into the car gas tank line. The vented gas cap has a one-way release valve that is pressure-activated. When the pressure reaches a certain point (defined by so many pounds per square inch) the valve opens by a very small amount, relieving some of the pressure. In this case, the pressure is formed on the outside of the tank, due to the vacuum formed from the displacement of fuel on the inside.