69 Fuel Cap Operation

[Greg L.]

This may seem like an odd question but how does the venting of the fuel cap work? Obviously its vented so that a vacuum in the tank isn't created as the fuel is pumped out but should it also be vented to prevent pressure build up inside the tank?

The reason I ask is because I did my initial road test today and noticed an odd sound coming from the fuel tank once it was back in the garage. I pulled the cap off and there was LOTS of pressure that was relieved. It's been 20 years since I started the restoration and I don't remember that type of pressure being in the tank.

The cap is a quality repop and it says VENTED on the top and there seems to be a small check valve in the middle. Should there be lots of pressure in the fuel tank after driving it?

Thanks

[Joe L.]

Re: 69 Fuel Cap Operation

This may seem like an odd question but how does the venting of the fuel cap work? Obviously its vented so that a vacuum in the tank isn't created as the fuel is pumped out but should it also be vented to prevent pressure build up inside the tank?

The reason I ask is because I did my initial road test today and noticed an odd sound coming from the fuel tank once it was back in the garage. I pulled the cap off and there was LOTS of pressure that was relieved. It's been 20 years since I started the restoration and I don't remember that type of pressure being in the tank.

The cap is a quality repop and it says VENTED on the top and there seems to be a small check valve in the middle. Should there be lots of pressure in the fuel tank after driving it?

Thanks

Greg-------

The cap contains a pressure-vacuum valve. However, the valve does not relieve pressure or vacuum at ambient. Once the limits of the valve are met, it relieves either pressure or vacuum.

So, what you are describing is completely normal. My 1969 has done it since the day it was new.

Stant is the only manufacturer of the 1963-74 Corvette fuel caps. Reproductions are actually the same parts that were used in PRODUCTION and once available from GM in SERVICE.

By the way, very late 1969's were equipped with fuel tanks which included an integral pressure-vacuum valve. Although all 1969's were equipped with a vented fuel cap, those late 1969's with the integral pressure vacuum valve can actually use the 1970-74 sealed cap. After the mid 1970's all GM SERVICE fuel tanks for 1963-69 Corvettes included the integral pressure-vacuum valve. GM instructed that when these tanks were installed, the sealed cap was also to be used.

[Greg L.]

Re: 69 Fuel Cap Operation

Okay, thank you very much Joe for clearing that up, much appreciated!