Gas Cap Identify Help
 

http://67-72chevytrucks.com/vboard/s...d.php?t=178829
I found the above post by Joesjunk from 2005. He was asking the same question I am. Reading his thread I still can't figure out what this cap fits. I have a gas cap GM3927086 and I don't know what it fits. Says "pressure vacuum" on the inside of the cap. Any help would be appreciated. Thanks

Re: Gas Cap Identify Help
 

What year is your truck? Half ton, or bigger?
'72s had a narrower fill neck diameter, and in 1/2 ton, had EEC emissions connections, like a return line from the carb, and a charcoal evaporator in the engine bay.
Earlier trucks and 3/4, and 1 tons didn't require emissions stuff.
Some gas caps were vented, some non-vented.
If you take the gas cap off, is there a whoosh?

Re: Gas Cap Identify Help
 

My truck is a half ton. The cap in question is a nos cap I have on the shelf and need to know what trucks it fits. I am clearing out my shelves so before I put this cap up for sale I'd like to have some more information. This is not a for sale thread. Thanks for your help

Re: Gas Cap Identify Help
 

Not sure on the part number, but can you post a picture of the front and back of it?

Re: Gas Cap Identify Help
 

See this thread beginning w post #46: https://67-72chevytrucks.com/vboard/...d.php?t=810278

Re: Gas Cap Identify Help
 

Pics of the cap

Re: Gas Cap Identify Help
 

one more photo. again this is not a for sale thread. thanks for your help.

Re: Gas Cap Identify Help
 

''Pressure Vacuum'' probably means Non-Vented.

Re: Gas Cap Identify Help
 

Found this... https://67-72chevytrucks.com/vboard/...d.php?t=818739

Re: Gas Cap Identify Help
 

Thanks all for the help.

Re: Gas Cap Identify Help
 

I found this when I googled the part number;
http://www.gmpartswiki.com/getpage?pageid=218675

Re: Gas Cap Identify Help
 

That would appear to make it a vented cap. I believe the vented caps for those years would hold 2 or 3 psi of pressure before venting air out of the tank. Hence the "Pressure Vacuum" stamping.
It was to keep fuel from sloshing out of the fuel fill when going around right hand corners when the tank is more than 1/2 full. My Burban has that problem as the locking cap I have isn't vented correctly.

Re: Gas Cap Identify Help
 

I quit using locking caps years ago. I found I lost more gas making hard rights than was ever likely to be siphoned out by theives. [The original use of the Canadian insult ''Hosers'' referred to gas siphon theives.]
Also when I lost the cap lock key, and had to musclef@%$ it off -- the neck was damaged and I wound up swapping in a '67 tank. After hot tanking it, painting the outside spraycan Aluminum and putting in a new float assembly.
And of course, the sender reads all different now.
The cap I have on the Stepside now goes ''Whoosh'' when I crack it open.