Original gas cap for...

[Ron]

I need an original gas cap for my '57 Ranch wagon (292 with 4 barrel), which I think is the same as used on the passenger cars.  I'm not looking for new or NOS, just an original used one that is not dented, damaged or rusty, etc., but still works well and looks reasonably good.  Please let me know what you have and the price.  Thank you, Ron...

[hiball3985]

Caps are different from the passenger car. Passenger car tanks are vented, Wagons and Rancheros aren't.

[gasman826]

All models except Wagons, Couriers, and Rancheros vented through a dedicated vent tube so the cap was NOT vented.  Wagons, Couriers, and Rancheros have no dedicated vent system so they have a vented cap.  The OEM caps vent air into the tank to eliminate vacuum caused by the removal of fuel.  The OEM caps also vented outward to the atmosphere to prevent pressure in the tank caused by heat build up.  I have a new, aftermarket cap on my wagon.  It works to seal the neck and keep gas from surging out of the tank.  It also allows air into the tank to neutralize any vacuum issues.  Unfortunately, the EPA band all venting of carburetors and fuel tanks to the atmosphere.  So far, I have NOT found a new, aftermarket gas cap that vents outward.  I occasionally have pressure build up in the tank to the point fuel will bypass the fuel tank/neck o-ring and leak gas.  Removing the neck and fabricating a dedicated vent system is on my winter to-do list unless someone finds a stash of NOS vented gas caps with fresh rubber gaskets.

[hiball3985]

The vented to the atmosphere caps were outlawed in the 70's. All the replacement caps only vent air inward to prevent a vacuum. I'd like to add a vent to my filler neck also but for now I just drilled a small 1/8 hole in the cap . Good luck finding an OEM cap....

[Ron]

Positively interesting how even the "small" posts like the one I started here can lead to such educational discourses.  In this case, vented vs non-vented caps and functions, etc.  For example, I didn't know that apparently non-vented gas caps came standard only on the wagons and the Rancheros, while all other models had vents coming off the gas-filler pipe.  I would guess the reason for the different applications is that the wagons have enclosed cabins all the way passed the gas filler tube, and the Rancheros have pretty much the same thing when an owner installs a shell on the bed.  Theoretically any gas fumes escaping from the vent could "possibly" find their way into the vehicles' interiors, thus no vents.  Anyway, yesterday I laid out a whopping $7 at Riley's for the gas cap pictured here that does not vent, but allows air in to prevent a vacuum.  It's made in Taiwan, of course, but it seems to fit and will do the job for now.  Thanks for all the great info, all!  Ron

[Ron]

Here are the other gas cap pictures that didn't get attached to the above post:

[RICH MUISE]

 "For example, I didn't know that apparently non-vented gas caps came standard only on the wagons and the Rancheros, while all other models had vents coming off the gas-filler pipe."

Ron...you have that backwards.
The non-vented caps were standard on all the passenger cars because the filler neck behind the license plate was too low to have a vented cap....gas would slosh out. Also, those passenger cars had vent tubes coming off the main body of the gas tank, not the filler neck.
The wagons, Rancheros,  came with vented caps because the filler necks were up high and there was no vent tube.

[hiball3985]

You may get by with one of the replacement caps depending on where you live and the temps. You wouldn't believe how much pressure my tank would build sitting in 100+- degrees and no way to vent..

[Ron]

Rich:  Thanks for that correction.  Continuing to learn here. 

Hiball:  How did you solve your pressure problem during high-temp weather?  Would drilling a small-diameter hole in the gas cap (on a wagon or Ranchero) solve the problem, or does it create safety issues?  When I got my wagon, it had an ill-fitting, after-market locking gas cap on it.  I'm now wondering if some PO put that on there intentionally because the cap's loose fit allowed the tank to vent on hot days, and to take in air as needed to eliminate vacuum problems. 

Ron

[gasman826]

Even in Michigan, gas coming out of an underground tank at 50-55 degrees into a 90 degree tank will swell up much more than water or air.  Occasionally, I've seen people duck when I release my cap.

[hiball3985]

Rich:  Thanks for that correction.  Continuing to learn here. 

Hiball:  How did you solve your pressure problem during high-temp weather?  Would drilling a small-diameter hole in the gas cap (on a wagon or Ranchero) solve the problem, or does it create safety issues?  When I got my wagon, it had an ill-fitting, after-market locking gas cap on it.  I'm now wondering if some PO put that on there intentionally because the cap's loose fit allowed the tank to vent on hot days, and to take in air as needed to eliminate vacuum problems. 

Ron

As mentioned in my other post I added a 1/8 hole. I can smell a slight vapor after the car sits in the garage over night. I don't have anything like a hot water heater in my garage. Fumes seem to dissipate after the door is open for a minute. Mine gets driven daily so it never sits in there long. Many people with early cars do this, I learned it on a Corvette site..