Gas cap options

[TotalChevy1]

I've been looking for a custom cap and think I may have found one, but somewhere I thought I read that 67-71 uses a different cap than the 72's, but this cap is listed on ebay and it say 67-72. Can anyone tell what the differences may be if any. I like the bowtie on the cap, but have had a hard time finding any.

[GMCBubba]

i dont' know the differences, but i did pick up a shiny plain jane cap from autozone. very cheap, very easy, in stock

[TotalChevy1]

Originally Posted by GMCBubba

i dont' know the differences, but i did pick up a shiny plain jane cap from autozone. very cheap, very easy, in stock

That's what I currently have but was looking to take it to the next level. I just can't rember what made the 72 different than 67-70. I'm not sure if it had to do with emmissions, because if it does I may be able to use, my truck didn't come with any emissions except PVC valve, no cat or air pump

[TotalChevy1]

ttt

[Olden Days]

I believe the difference is that in 71, 72 with the emissions stuff added they used a non vented cap. prior to that would have been vented.

I just found that auction. That is a nice looking but spendy cap. His description states it goes up to year 70 so I would assume it is a vented cap

[TotalChevy1]

Your right ..it is a little on the expensive side. Would there be any side effects with the fuel system, if one was used on a none vent system.

[Longhorn Man]

All these trucks came with emissions control, every one built.
In 71, all trucks had a return line and charchol canister, and required a different cap from 70 and older. I *think* the older ones were vented, and the later ones were not. That, or the other way around.

[TotalChevy1]

Originally Posted by Longhorn Man

All these trucks came with emissions control, every one built.
In 71, all trucks had a return line and charchol canister, and required a different cap from 70 and older. I *think* the older ones were vented, and the later ones were not. That, or the other way around.

Is the canister at the fuel pump? there are two fuel line to the fuel pump. Is the purpose of the cap to keep the system under presure? If so, what would happen if you used a vented cap?

[ChevLoRay]

Several years ago, Custom Truck magazine had an article that was intended to showcase the options for our trucks. One picture showed a stock gas cap, the stainless steel version, and stated that it was very rare to see one due to so many of them getting lost at the filling stations over the years. I still have mine but replaced it on 9-11-01 with a locking NAPA cap.....call it panic at the time due to the uncertainty of the moment.

But they said stock stainless gas caps were rare. Geeze, whodathunk?

[68caliRat]

Originally Posted by Longhorn Man

All these trucks came with emissions control, every one built.
In 71, all trucks had a return line and charchol canister, and required a different cap from 70 and older. I *think* the older ones were vented, and the later ones were not. That, or the other way around.

When you say "everyone" I think smog pumps and cats, mine is stock(been in the family almost since new, and only has a PCV. Which runs to the spacer between the carb and air cleaner. Other than that...NADA.

[Olden Days]

Originally Posted by Longhorn Man

All these trucks came with emissions control, every one built.
In 71, all trucks had a return line and charchol canister, and required a different cap from 70 and older. I *think* the older ones were vented, and the later ones were not. That, or the other way around.

The return line and charchol canister was the "added" emissions I was talking about, which is why it needs the non vented cap.

TotalChevy. If you have to pass an emission test it wont pass with a vented cap but otherwise you can run it

[TotalChevy1]

Originally Posted by Olden Days

The return line and charchol canister was the "added" emissions I was talking about, which is why it needs the non vented cap.

TotalChevy. If you have to pass an emission test it wont pass with a vented cap but otherwise you can run it

We'll I just keep the other cap for emissions. I've been doing a little reading and the general opinion is all 72's came with emissions. When I came home I checks and this truck never had a charcoal canister, the fue tank doesn't even have the lines on it. There no signs the tank has evey been taken out. The orginial owner never changed anything on this truck, so I trying to figure this mystery out. All it's had is a PVC....no cat, no air pump....could this be

[Longhorn Man]

i think the canister is in the fenderwell or something. Never bothered looking for it.
I *THINK* if you used a vented cap, then the stored fumes in the charchol canister wouldn't get sucked out properly?
If that's not right, than I have no clue.

[Longhorn Man]

99% of the ones you see today are chrome, not stainless

[TotalChevy1]

Originally Posted by Longhorn Man

99% of the ones you see today are chrome, not stainless

How do you determine if they are stainless, my has a shine to it, but when you us a metal cleaner it turns the rag black

[70c10]

I recently put a brand new 71/72' cap (didn't realize it) on my dad's 70' and it wouldn't run!. I started chasing my tail because I couldn't figure out what the heck was wrong with his truck. I then remembered that the caps were different and verified it in a parts catalog. I put his old cap back on and the truck roared to life! Be careful and keep this in mind in case this happens after swapping caps!

[Longhorn Man]

Originally Posted by TotalChevy1

How do you determine if they are stainless, my has a shine to it, but when you us a metal cleaner it turns the rag black

that would be stainless then

[Longhorn Man]

the air cleaner with snorkle is a smog item
the PCV
The hose going to the carb from the valve cover
the ECS crap
the heat riser leading to the air cleaner from the manifold
All these are emissions control items.
Smog control began in 64 in cars... I think started on GM trucks a few years later.

[68caliRat]

Must be, I just don't see how it would significantly reduce the emissions from my truck...seems like a waste..