1970 fuel cap ??

[fotyfobravo]

Original 1970 1500 GMC truck. I have bought 2 replacement fuel caps. BOTH seem to be vented. But .... After about 10 minutes the engine stalls out and I remove the fuel cap and....wooosh....the air rushes into the filler and then the truck will crank again. If the cap doesn't vent, a vacuum is created in the fuel tank as the fuel is pumped to the engine.

Is there another vent other than the cap that might be plugged up? I have looked under the cab and only see ONE fuel line leaving the tank and running forward to the fuel pump.

Thanks y'all....

[volksworld]

nope...no other lines...the cap is it...maybe one of the vendors here have ones that actually work

[gmc 2500 4x4]

vapor lock? collapsed hose?

[697498chevy]

I replaced the gas tank on my 1969 C 10 , but I found a Car Quest cap #10623 worked best for me . About 7 bucks , I think .

[fotyfobravo]

Thanks for the replies! Thats what I thought. I will pick up a new 10623.

[mr48chev]

I had the same problem with Stant brand gas caps several years ago. Took two back before I got one that was actually vented. Walked to the gas station and got gas and walked back the first time it happened. Truck quit on the same corner on the way to work three days in a row.

[697498chevy]

First cap I tried leaked gas . Second cap didn't leak , but built up a lot of tank pressure . #10623 cap doesn't leak or build up any pressure . Hope it works for you .

[fotyfobravo]

I took the advice and bought the Carquest 10623. Fixed it! Thanks!

[alsriv2]

That is good news...both for a good part number for others to have and that you have a solution for your venting issue.
Recently I had a venting issue with my '69. New vented cap from Napa and another from Autozone. Comes to find out my cap would hold the tank pressure in...and would not vent at all. I ended up disassembling the cap to gain access to the internal spring and kept cutting the spring a bit at a time until I had no leaks and the cap would vent pressure correctly. So far its worked and overall I cut the spring about 1/2 its normal length.

[fotyfobravo]

Originally Posted by alsriv2

That is good news...both for a good part number for others to have and that you have a solution for your venting issue.
Recently I had a venting issue with my '69. New vented cap from Napa and another from Autozone. Comes to find out my cap would hold the tank pressure in...and would not vent at all. I ended up disassembling the cap to gain access to the internal spring and kept cutting the spring a bit at a time until I had no leaks and the cap would vent pressure correctly. So far its worked and overall I cut the spring about 1/2 its normal length.

Exact same parts for me....the 10623 seems to be venting properly!

I was shocked that the Napa cap wouldn't breath.

[fotyfobravo]

Originally Posted by volksworld

nope...no other lines...the cap is it...maybe one of the vendors here have ones that actually work

I noticed you "signature" says short bed leaf spring. I look all over at 67 to 72 short bed trucks. It seems rare to see the leaf spring rear end vs the trailing arms. Most are trailing arms. Mine is a GMC short bed fleetside with 6 lug and leafs.

Is it rare or just a GMC thing??

[697498chevy]

Glad the #10623 cap worked for you .