Help to ID C2 gas cap

[Wayne K.]

Found this original looking gas cap. I'm sure it is a C2 cap. Anyway to tell what year?

[Timothy B.]

Re: Help to ID C2 gas cap

Wayne,

The 63 cap is not supposed to have a valve so if you blow through the hole it vents right to atmosphere, I think the 64-69 caps are the same in that there is a pressure valve that prevents fumes unless pressure builds up too high inside the tank.

[Joe L.]

Re: Help to ID C2 gas cap

Found this original looking gas cap. I'm sure it is a C2 cap. Anyway to tell what year?

Wayne-----


It's one of these:

GM #3830983------1963 Z-06 only

GM #3843576------1964-68


Considering the above, I think you can feel pretty confident that it's a GM #3843576.

[John D.]

Re: Help to ID C2 gas cap

Wayne, The cap is not a 63 as they are on their own. My 9900 car has the original gas cap. It has a small hole in the underside of the cap. The 5th edition says approx 1963 vin 9000 through the end of 64 also have the small hole, but use a series of internal valves to release pressure to the atmosphere. The 2nd style cap has a "sm" logo with two circles on the reverse side. I don't know if my cap has this or not. But never the less your cap is not 63 or 64.

I just checked my 9900 63 cap and saw that it does in fact have the logo with two circles and the plain small hole. So it must have the internal valves in it also Tim???

[Harry S.]

Re: Help to ID C2 gas cap

Ok, someone please post a picture of a 63 cap.

[Joe L.]

Re: Help to ID C2 gas cap

Wayne, The cap is not a 63 as they are on their own. My 9900 car has the original gas cap. It has a small hole in the underside of the cap. The 5th edition says approx 1963 vin 9000 through the end of 64 also have the small hole, but use a series of internal valves to release pressure to the atmosphere. The 2nd style cap has a "sm" logo with two circles on the reverse side. I don't know if my cap has this or not. But never the less your cap is not 63 or 64.

I just checked my 9900 63 cap and saw that it does in fact have the logo with two circles and the plain small hole. So it must have the internal valves in it also Tim???

John-----

If you look closely at the photo, you will note that the hole on the underside has a tiny "crimped-over flange" around the hole. This indicates that it has the internal pressure/vacuum valve and, therefore, is one of the 2 part numbers I mentioned. The 1963-only caps without the internal valving have a "plain old hole" with no evidence of a "crimped over flange".

Also note the "raised" area surrounding the hole on the cap pictured. This area serves as the seat for an internal spring that is part of the pressure/vacuum valve. The 63-only cap with no internal pressure/vacuum valve does not have this raised area---I believe it tapers evenly from the outer perimeter to the center

[Michael H.]

Re: Help to ID C2 gas cap

Wayne,

The 63 cap is not supposed to have a valve so if you blow through the hole it vents right to atmosphere, I think the 64-69 caps are the same in that there is a pressure valve that prevents fumes unless pressure builds up too high inside the tank.

If I remember correctly, you can hear the flapper in a late 63 through 68 cap if you shake the cap???
I've never had one apart so I'm not sure about this.

[John A.]

Re: Help to ID C2 gas cap

Part# 3820865 was "vented", basically just a small hole through the cap and was used in early 63. Per Noland Adams book these were still in use till about ser# 17000.
The later 63-67 cap was #3843576 and it has a spring (valve) inside so if you push on the bottom of the cap it will give a bit. It was put into production in early 63 (AIM date 2-22-63)

[Timothy B.]

Re: Help to ID C2 gas cap

I justed checked the cap on my 63 and it's like the one pictured. I know the cap has the circles and logo and the embossment for a valve seat. If I blow through the hole it does not vent so there must be a valve.

I would like to see a pic of a real 63 cap also as I thought mine is original to the car. As soon as the cap is removed there is a naturally a strong smell of gas so that valve IS a good thing. I can't believe GM made a gas cap vented directly to atmosphere, what is gas cap on 62 and earlier cars like.

[Jack H.]

Re: Help to ID C2 gas cap

Here's a closeup of the bottom of an early '63 gas cap. Joe Lucia already mentioned the 'give away' of the presence of a crimp ring around the vent hole indicating '63L and up versions of the vented gas cap....

[Wayne K.]

Re: Help to ID C2 gas cap

Wayne-----


It's one of these:

GM #3830983------1963 Z-06 only

GM #3843576------1964-68


Considering the above, I think you can feel pretty confident that it's a GM #3843576.

Should I be able to find a part# on the cap? When I blow through the hole I can hear air escape and when I shake it something rattles. Does that mean it is not functional anymore? I haven't tried pushing over the hole as someone has suggested but will tonight. Thank you for all the replies to date.

Wayne

[Timothy B.]

Re: Help to ID C2 gas cap

Jack,

Thanks for that picture of the cap, I don't believe I have seen one before, now to find one for my car.

[Harry S.]

Re: Help to ID C2 gas cap

I have mine apart as I will be replating the cap. Since I'm not the original owner of the car it may or may not be original to an April 20th car.

This must be the 63L version. The one way spring loaded valve, allows air into the gas tank. The larger spring is there to force a good seal between the cap and the tank.

[Stuart F.]

Re: Help to ID C2 gas cap

My original 63 cap s/n# 19,*** has just the plain vent hole w/GM circled logo inside, which is why I replaced it with the later replacement cap that has the two way valve (vent/pressure relief) this past summer when I was having fuel percolation problems (didn't help much). As I ran the test to see if I heard any pressure release when I took the cap off, and I did, I enlarged the hole slightly in my original as advised (and that didn't help much). So now I've screwed up my original, my replacement doesn't help, and I learned anyone can remove my locking cap with a nickle! Not a very productive summer in that department.

Stu Fox

[Harry S.]

Re: Help to ID C2 gas cap

Stu, I've done a pressure test on that valve and it only lets air go in one direction, into the tank. I imagine this is to allow air to take the place of the gas as it used. It does not allow excess pressure in the tank out.