Gas Cap for a 1968

[Sean S.]

Guys,

Our '68 has an old school, locking, dealer-installed-type gas cap.
It came with the car when we became the new caretakers a few years ago.

When the car sits in the garage uncovered, there are gas fumes released from the gas fill area.
When a cover is on the car, they are not quite as noticable.

Upon inspecting the cap, there is not any kind of rubber gasket to help seal the cap to the filler neck. I don't even see where there would have been one.

Also, I read a post on the TDB, that the locking caps weren't good for driving, as they tend to leak gasoline.

I was going to replace with the stock cap. The TIM states the cap is stamped VENTED (on the top?), and SM inside a C on the bottom. Some have paper gaskets, some rubber. Car is a 3/4/68 birthday.

Prefer a good used original vs. a reproduction.
Is there a part# to look for? Or anything to qualify a '68-correct cap from other years?
I would assume even though this is a vented cap, gas fumes would be less noticable than what I've got now in the locking cap with no gasket.

Thanks
Sean

[Joe L.]

Re: Gas Cap for a 1968

Guys,

Our '68 has an old school, locking, dealer-installed-type gas cap.
It came with the car when we became the new caretakers a few years ago.

When the car sits in the garage uncovered, there are gas fumes released from the gas fill area.
When a cover is on the car, they are not quite as noticable.

Upon inspecting the cap, there is not any kind of rubber gasket to help seal the cap to the filler neck. I don't even see where there would have been one.

Also, I read a post on the TDB, that the locking caps weren't good for driving, as they tend to leak gasoline.

I was going to replace with the stock cap. The TIM states the cap is stamped VENTED (on the top?), and SM inside a C on the bottom. Some have paper gaskets, some rubber. Car is a 3/4/68 birthday.

Prefer a good used original vs. a reproduction.
Is there a part# to look for? Or anything to qualify a '68-correct cap from other years?
I would assume even though this is a vented cap, gas fumes would be less noticable than what I've got now in the locking cap with no gasket.

Thanks
Sean

Sean------

As far as the gasoline odor goes, you're going to get some of it even with a standard gas cap. Gasoline vapors can vent from the tank but they also emanate from the carburetor. 1968 was before the advent of evaporative emissions control (EEC). See, emissions controls actually do have some practical benefit for the car owner.

As far as the locking gas cap goes, it originally had a rubber seal. It must have come off at some point. I would not use one of these on the road with or without the seal.

Two different gas caps were used for 1968. The early version, GM #3843576, was the same as used for L1963 through 1967. This cap had a brown cellulosic (paper) seal. However, by the time that your car was built, I believe the later cap, GM #3921689, was in use. I'm pretty sure this cap used a neoprene (rubber) seal. Both of these caps are long-since GM-discontinued.

For 1969, cap GM #3952708 was introduced and it quickly became the SERVICE cap for all 1963-68 applications. If there is any difference between a GM #3921689 and the GM #3952708, I don't know what it is. It's possible the difference involves some internal components of the pressure/vacuum release system which can't be seen. The GM #3952708 has been recently discontinued. However, you might still find some around. Also, it's still available in "reproduction" and manufactured by the original supplier to GM, Stant Manufacturing. From what I've seen, the current "reproduction" is identical to the original 3952708 as one would expect since it's made by the same manufacturer.

[Jim T.]

Re: Gas Cap for a 1968

I have had a GM locking vented gas cap with its intact gasket in use since 1973 on my 1968 with no problems. Have not noticed any gas fumes in the garage where the 1968 spends most of it's time. I was in the garage today for 4-5 hours finishing the installation of the gauge panel and the 68's radio. Have a full tank of gas. Still have the original gas cap for a back-up if needed.

[Sean S.]

Re: Gas Cap for a 1968

Joe, Jim,
Thanks for your replies. Good information.
Have found a couple of good examples online.
Will replace with the correct cap and keep the locking cap for shows, etc.
Have a great weekend. Wish I was in Carlisle, PA.
Sean

[Joe R.]

Re: Gas Cap for a 1968

Sean,

Paragon is the supplier of the original vented 708 produced by Stant with the correct "S" stamped inside and a seal that will not allow fumes to fill your garage.

JR

[Douglas L.]

Re: Gas Cap for a 1968

Heres a few pics of the cap from my Jan 15 build 68. Cant be sure it the factory one but patina leads me to believe its possible. It has a rubber seal. Hope it helps, DougIMG_2047.JPGIMG_2048.JPGIMG_2053.JPG