Converting vented to non vented gas cap

[Joe L.]

Re: Converting vented to non vented gas cap

Joe -

I think the (vented) cap shown in P&A for '57-'62 is a long-running error. We know for a fact that only four caps were ever released and used in production, and all of them were of solid riveted construction, with no valves or vents of any sort (the drawings are in Noland's book):

#3742472 was used from mid-'57 through mid-'58

#3751022 was used from mid-58 through 1962

#3751027 was used from '61 through '62

#3764641 was used from mid-'58 through 1962

Another cap, #3787292, was released for Service use only on a TSB in November, 1960, which was identical to the #3764641 except it used a 2-way pressure/vacuum valve to prevent leakage and provide venting; this cap was never used in production. Why it was stocked for the TSB (which dealt with fuel leakage) is something of a mystery, as the tank didn't need a vented cap - it was already vented, starting in mid-'57.

The use of a solid non-vented cap (as used in production) has been well-known for many years as the only cure for '57-'62 fuel leakage at the cap; many vendors sell a vented cap for '57-'62 usage (maybe due to the vented cap in the P&A), and all of them leak fuel.

John------


As you say, as a mistake it's definitely a long-running one. All of the caps you mentioned were also once available in SERVICE except for the GM #3764641. I cannot find that it was ever available in SERVICE.

The GM #3787292 first showed up in about 1960. It replaced the GM #3772749 which had replaced the GM #3751027 in August, 1960. I believe the 3772749 was a vented cap. If so, when it replaced the GM #3751027 is when the "diversion" from a non-vented to a vented cap occurred for SERVICE.

In May, 1961 the GM #3787292 was discontinued and replaced by the GM #3787291. The latter was discontinued in June, 1962 and replaced by the GM #3814436.

The GM #3814436 lasted a long time until August, 1984 when it was discontinued and replaced by the GM #14002439 which continues to be available.

It is very possible that the aftermarket is basing their application information on the GM information which is, apparently, incorrect. I have seen the same sort of thing happen before with respect to other parts. When GM gets it wrong, the aftermarket follows suit. Fortunately, GM doesn't get it wrong too often.

In any event, as a cataloging error, this one has persisted uncorrected for over 50 years!

[Joe L.]

Re: Converting vented to non vented gas cap

Joe -

I think the (vented) cap shown in P&A for '57-'62 is a long-running error. We know for a fact that only four caps were ever released and used in production, and all of them were of solid riveted construction, with no valves or vents of any sort (the drawings are in Noland's book):

#3742472 was used from mid-'57 through mid-'58

#3751022 was used from mid-58 through 1962

#3751027 was used from '61 through '62

#3764641 was used from mid-'58 through 1962

Another cap, #3787292, was released for Service use only on a TSB in November, 1960, which was identical to the #3764641 except it used a 2-way pressure/vacuum valve to prevent leakage and provide venting; this cap was never used in production. Why it was stocked for the TSB (which dealt with fuel leakage) is something of a mystery, as the tank didn't need a vented cap - it was already vented, starting in mid-'57.

The use of a solid non-vented cap (as used in production) has been well-known for many years as the only cure for '57-'62 fuel leakage at the cap; many vendors sell a vented cap for '57-'62 usage (maybe due to the vented cap in the P&A), and all of them leak fuel.

John------


One other thing that's been troubling me about this: whether or not the vented cap is required for 57-62 Corvettes, I don't understand why the vented cap leaks gasoline when used for 57-62. Whether a cap is vented or non-vented it should not leak gasoline. Certainly, many other GM cars did use and require a vented cap, even the same ones specified in SERVICE for Corvettes. Did all of these leak gasoline, too? I can't see why it would be any different for them versus Corvettes.

1963-69 Corvettes all used a vented cap and, unless the seal had failed, I've never seen one of those caps leak gasoline. They do expel slight gasoline vapors under certain conditions but the 57-62 Corvettes are otherwise vented in the gas filler area. So, if vapors were expelled from the tank there would be no way of knowing if it was emanating from the vent tube or a vented gas cap.

To me, if the C1 Corvettes using vented gas caps leak fuel it sounds more like a problem with a defective cap than it does as something fundamental to the fact that they are a vented cap.

[John H.]

Re: Converting vented to non vented gas cap

John------


One other thing that's been troubling me about this: whether or not the vented cap is required for 57-62 Corvettes, I don't understand why the vented cap leaks gasoline when used for 57-62. Whether a cap is vented or non-vented it should not leak gasoline. Certainly, many other GM cars did use and require a vented cap, even the same ones specified in SERVICE for Corvettes. Did all of these leak gasoline, too? I can't see why it would be any different for them versus Corvettes.

1963-69 Corvettes all used a vented cap and, unless the seal had failed, I've never seen one of those caps leak gasoline. They do expel slight gasoline vapors under certain conditions but the 57-62 Corvettes are otherwise vented in the gas filler area. So, if vapors were expelled from the tank there would be no way of knowing if it was emanating from the vent tube or a vented gas cap.

To me, if the C1 Corvettes using vented gas caps leak fuel it sounds more like a problem with a defective cap than it does as something fundamental to the fact that they are a vented cap.

Joe -

Early ('53-mid-'57) C1's always had an issue of fuel leakage, especially on hard right turns with over 1/2 a tank of fuel, and during that era they used a vented cap. At the same time the running production change was made in mid-'57 to add a vent tube and hose to the tank and use a new non-vented cap to deal with the problem, a Chevrolet Service Letter was issued to the dealers with detailed instructions on how to add that vent tube and hose to the tank and use the new non-vented cap to deal with customer complaints of fuel leakage and odors; this was no simple job, as it required removal of the tank, drilling a hole, soldering in the tube, etc.

The vented tank and non-vented cap solved that problem for the next 5-1/2 years, so I can't imagine why a vented cap would be released for Service use, but it was.

[Joe M.]

Re: Converting vented to non vented gas cap

I converted my vented cap to non-vented by pouring a drop of epoxy into the vent hole on the back side of the cap. Let it harden and it will not be a vented cap after that.

[Bill M.]

Re: Converting vented to non vented gas cap

Joe -

Early ('53-mid-'57) C1's always had an issue of fuel leakage, especially on hard right turns with over 1/2 a tank of fuel, and during that era they used a vented cap. At the same time the running production change was made in mid-'57 to add a vent tube and hose to the tank and use a new non-vented cap to deal with the problem, a Chevrolet Service Letter was issued to the dealers with detailed instructions on how to add that vent tube and hose to the tank and use the new non-vented cap to deal with customer complaints of fuel leakage and odors; this was no simple job, as it required removal of the tank, drilling a hole, soldering in the tube, etc.

The vented tank and non-vented cap solved that problem for the next 5-1/2 years, so I can't imagine why a vented cap would be released for Service use, but it was.

Maybe. My father made a list of complaints with his brand new '59, one of which was "Fuel spurts out of tank on hard right turns." The original cap is long gone, replaced by a locking cap, so I don't know which cap it had originally.

Do I remember correctly that the '61-'62 tank had baffles? Don't know if the baffles were for a leak, just for sloshing, or maybe for both...

My planned fix is to incorporate a loop in the vent hose when I get the '59 back on the road. The original vent hose is a straight shot from the vent to the filler door.

[John H.]

Re: Converting vented to non vented gas cap

My planned fix is to incorporate a loop in the vent hose when I get the '59 back on the road. The original vent hose is a straight shot from the vent to the filler door.

Bill -

I wrote a comprehensive photo-illustrated article in the Restorer a year or two ago (maybe three) on solving/fixing the C1 fuel odor/spillage problem; don't recall the specific issue offhand.

[Jim D.]

Re: Converting vented to non vented gas cap

I converted my vented cap to non-vented by pouring a drop of epoxy into the vent hole on the back side of the cap. Let it harden and it will not be a vented cap after that.

That's exactly what I did with the vented cap on my 1960.

[Bill M.]

Re: Converting vented to non vented gas cap

Bill -

I wrote a comprehensive photo-illustrated article in the Restorer a year or two ago (maybe three) on solving/fixing the C1 fuel odor/spillage problem; don't recall the specific issue offhand.

Thanks, John. It's in Vol. 34, no.2, Fall 2007.

I'll make sure I follow all your recommendations.

(I don't know if the fuel spurting from my father's new '59 was fixed by the dealer...)

Bill

[Ian G.]

Re: Converting vented to non vented gas cap

Great Thread. Thought I'd add some info that may be of interest, gleaned by sleuthing my 59 parts book and a cap schematic I found.

Info we know: The 1958-60 judging guide shows the Fuller Emerson, Eaton and Stant caps as correct for mid 58-60 cars (I don't have a 61-62 guide). I have a schematic (attached) that shows the Following caps/part number combos:

#3751022 Stant
#3751027 Fuller Emerson
#3764641 Eaton

I have a 1959 GM Parts book dated April 1959 with running changes till Nov 1959. #3751027 (F&E) is listed in grp 3.028 as the designated gas cap at that time. At the back of it in the running changes section, a change dated Dec 1958 lists the 3751022 (Stant) cap to be mixed with 3751027. The #3764641 cap isn't mentioned in the book, but some unscientific perusal of running change dates/part numbers made me think that number was done in Dec 1958, vs earlier - though it could have been later. I imagine the numbers were assigned more or less in order for the most part. That's just speculation on my part though.

Now, the 59 AIM shows the 3751022 & 3764641 added on Dec 7, 1958.

So in any event, based on that, I'm of the opinion that for Late 58 & early 59 Corvettes may only have used the 3751027 (F&E) cap till between Oct & Dec 58, at which point the Stant cap (and possibly the Eaton cap) was mixed in, when they saw they couldn't get enough F&E caps. Maybe the 3764641 wasn't used over the counter in SERVICE at that point, though it was used on the line.

Joe, do you have a 1960 parts book you can see if the 3764641 is mentioned at the back as being mixed in with #3751027?

57_60_gas_caps.jpg

[Joe L.]

Re: Converting vented to non vented gas cap

Great Thread. Thought I'd add some info that may be of interest, gleaned by sleuthing my 59 parts book and a cap schematic I found.

Info we know: The 1958-60 judging guide shows the Fuller Emerson, Eaton and Stant caps as correct for mid 58-60 cars (I don't have a 61-62 guide). I have a schematic (attached) that shows the Following caps/part number combos:

#3751022 Stant
#3751027 Fuller Emerson
#3764641 Eaton

I have a 1959 GM Parts book dated April 1959 with running changes till Nov 1959. #3751027 (F&E) is listed in grp 3.028 as the designated gas cap at that time. At the back of it in the running changes section, a change dated Dec 1958 lists the 3751022 (Stant) cap to be mixed with 3751027. The #3764641 cap isn't mentioned in the book, but some unscientific perusal of running change dates/part numbers made me think that number was done in Dec 1958, vs earlier - though it could have been later. I imagine the numbers were assigned more or less in order for the most part. That's just speculation on my part though.

Now, the 59 AIM shows the 3751022 & 3764641 added on Dec 7, 1958.

So in any event, based on that, I'm of the opinion that for Late 58 & early 59 Corvettes may only have used the 3751027 (F&E) cap till between Oct & Dec 58, at which point the Stant cap (and possibly the Eaton cap) was mixed in, when they saw they couldn't get enough F&E caps. Maybe the 3764641 wasn't used over the counter in SERVICE at that point, though it was used on the line.

Joe, do you have a 1960 parts book you can see if the 3764641 is mentioned at the back as being mixed in with #3751027?

[ATTACH=CONFIG]46339[/ATTACH]

Ian------


The GM #3764641 is not found anywhere in the 1960 P&A catalog. I doubt that it was ever available in SERVICE

[Ian G.]

Re: Converting vented to non vented gas cap

Thanks for confirming that Joe. Correction, the AIM shows the three caps being used from Oct 7, 1958. That's what I was thinking the mix entry meant... the Stant and F&E caps were interchangeable in SERVICE, but not the Eaton. I occasionally see NOS Stant and F&E caps, but Eaton ones - not so much.

[Joe M.]

Re: Converting vented to non vented gas cap

The Feb. 1, 1961 edition of P&A only shows one cap for 57-61 Corvettes and station wagons, a cap with "vented valve", 3787292. Apparently by early 1961 the non-vented caps were no longer in service.

[Joe M.]

Re: Converting vented to non vented gas cap

After reading the 2011 part of this thread, I see that the consensus is that the vented cap was never a service part, just a long running error in the P&A books.

[Ian G.]

Re: Converting vented to non vented gas cap

Hey Joe M., I think what Joe L. and John H. are saying is the non-vented cap solved the early fuel leakage problem, so it was a mistake to put the vented cap as the SERVICE replacement, as they reintroduced the fuel leakage problem. At least that's what I got out of it..

[John F.]

Re: Converting vented to non vented gas cap

Here is a pic of the vent line on a 62 tank. Cap in not vented.