1970 gas cap

[D S.]

I know the 1970-1972 JG states that the gas caps are supposed to have SEALED on them but my March build 1970 has a VENTED cap on it that I believe to be original. Another early build 1970 LT-1 owner says his Corvette has what he believes to be an original cap that also has VENTED on it. Could these have carried over from the 1969 production year? To be "correct" I did find an original SEALED cap in nice condition but am curious about this.

Thanks,
Scott

[Jim T.]

Re: 1970 gas cap

Scott my original owner 1970 Corvette is July built and has the original sealed type gas cap. Gives a release of build up pressure when the cap is released. Always has.
The GM locking gas cap, chrome finish, I bought in 1970 is also not vented.

[Chris L.]

Re: 1970 gas cap

My 70 with a Feb build date has the original cap on it and it is a sealed cap.
Chris

[Joe L.]

Re: 1970 gas cap

I know the 1970-1972 JG states that the gas caps are supposed to have SEALED on them but my March build 1970 has a VENTED cap on it that I believe to be original. Another early build 1970 LT-1 owner says his Corvette has what he believes to be an original cap that also has VENTED on it. Could these have carried over from the 1969 production year? To be "correct" I did find an original SEALED cap in nice condition but am curious about this.

Thanks,
Scott

Scott-----


I really doubt that any 1970 Corvettes were originally built with a vented fuel cap. For something as "portable" as a fuel cap, it would be virtually impossible to document originality of a vented cap found on a 1970 unless one had control over the car since day-one.

[Jack H.]

Re: 1970 gas cap

I have a vague recollection that there were several PN's for the Corvette gas cap in 1970 (running changes) and some of these MAY have been related to the NA-9, California emission option. But, one would have to look at the AIM book and its drawing revision tables. Then, translate GM PN's into specific gas cap construction details.

Remember, while California constituted roughly 10-15% of total Corvette production/consumption, we RARELY see factory original NA9 equipped cars... It's as if, prior owners removed various components of the NA9 system and current owners/restorers decided NOT to research the car's origin history and restored it to the 49-State configuration where parts are easier to find because they were more plentiful.

[Chris L.]

Re: 1970 gas cap

Can someone explain what the advantage or resaon for the sealed cap versus a vented cap? Thanks
Chris

[Joe L.]

Re: 1970 gas cap

Can someone explain what the advantage or resaon for the sealed cap versus a vented cap? Thanks
Chris

Chris-----


1963-L69 fuel tanks had no integral pressure or vacuum relief valves. So, necessary pressure and vacuum relief functions were built into the fuel caps.

In late 1969 an integral pressure and vacuum relief valve was incorporated into the Corvette fuel tank. So, no pressure or vacuum relief function was necessary in the cap. However, 1969 Corvettes continued to use "vented" type caps right to the end of the model year.

The integral pressure/vacuum valve continued to be used from 1970 through 1974. No pressure/vacuum relief function was necessary for the fuel cap and a "sealed" cap was used. Actually, the 70-74 cap is not COMPLETELY sealed. It is designed to relieve pressure at a certain PSI if the integral pressure/vacuum valve fails. There is no back-up that I know of for the vacuum relief function built into the 70-74 caps, though.

[Chris L.]

Re: 1970 gas cap

Joe..thanks for the explanation....not sure I understand fully, but if the "sealed" cap comes lose while driving, does this present a problem. Reason I ask is a few times when refueling I have found my cap lose as if it had just been set down on the filler opening. It still ran fine, but I am curious if this could be a potential "breakdown" somewhere down the road. Thanks
Chris

[Terry M.]

Re: 1970 gas cap

My late January built 1970 (no NA9) came with a SEALED cap, which I still have.

The only danger if the fuel cap comes loose, is spilled fuel if the tank is full enough.

[Jim T.]

Re: 1970 gas cap

Chris my 70's sealed cap is very secure, takes an slight effert to remove it and install it. Fits really tight and just turning it very little will let the pressure out when it is being removed.
How is your gas level from night to morning or next drive? Could someone be removing a few gallons and just laying the cap back on to keep the noise down?

[Chris L.]

Re: 1970 gas cap

Mine is very tight also and when I tighten it after fueling it wants to kick back almost like it has a spring in it!. FUel level stays the same as it is coverd and locked in a garage 24/7 !! Thanks
CHris

[Jack H.]

Re: 1970 gas cap

It does have a spring in it... The inside portion of the cap can move in/out relative to the outer portion of the cap. That's what keeps the cap snug on the tank filler neck and it's how the cap achieves its emergency venting function.

[Joe L.]

Re: 1970 gas cap

Joe..thanks for the explanation....not sure I understand fully, but if the "sealed" cap comes lose while driving, does this present a problem. Reason I ask is a few times when refueling I have found my cap lose as if it had just been set down on the filler opening. It still ran fine, but I am curious if this could be a potential "breakdown" somewhere down the road. Thanks
Chris

Chris-----

The 63-74 fuel cap and filler neck use a "cam lock" system as the primary locking and retention mechanism. I suppose if the filler neck cam lock were excessively worn or damaged, that could cause the fuel cap to loosen while driving, although I've never heard of this. Also, I suppose if the fuel cap retaining lugs were worn or damaged that could cause the problem, also. Once again, I've never experienced or heard of such a problem.

Failure of the filler cap to be fully tight will not cause any sort of "breakdown". The most that will be caused in a vehicle operational sense is the spillage of fuel and gasoline fumes in the passenger compartment. Of course, spillage of fuel ALWAYS presents a serious compromise to safety.

[Terry M.]

Re: 1970 gas cap

I would think if the spring inside the cap failed, as it might if someone tried to plate the entire cap without dissassembly, the cap might come loose during driving.