Gas Tank Cap

Subject: Gas Tank Cap Thu Jun 17, 2010 10:31 pm

Is it vac-only, or is there a relief valve?
Green books say your results may vary.

1984 244 B21FT inter cooled.

Subject: Re: Gas Tank Cap Fri Jun 18, 2010 9:48 pm

Should be pressure tight. Excess pressure should get vented through the charcoal canister.

Number of posts : 1902 Registration date : 2010-05-07

i am wondering if there is some sort of tool to re-form the ovalized aluminum filler neck into a nice circular shape. if not we need to invent it

Subject: Re: Gas Tank Cap Mon Jun 21, 2010 4:23 pm

Sounds possible, but I'm curious about the necessity.

To follow up, with the particular emissions crap on this car, I've figured that the gas cap IS supposed to have a relief valve at atmospheric. Below that it goes to the can, above that it vents.

If its vac only like my cap, th fumes find a way on a hot day.

Subject: Re: Gas Tank Cap Mon Jun 21, 2010 10:23 pm

I put the new style on for the test,

and use a nice JY metal original for DD'ing.

At $1.99 it's one of the best deals going at PnP.

Subject: Re: Gas Tank Cap Thu Jun 24, 2010 9:46 am

Sure that's not the other way around, above atmospheric it vents through the can and allows it to suck in at vac?

All the ones I've seen have no releif valves.

Subject: Re: Gas Tank Cap Thu Jun 24, 2010 11:21 am

I think it works as kind of an emergency vent.
This came from the emissions control systems greenbook.
Eh. When I started looking at late cars in the JY, they had relief valves.
That's not really science, but; well I'm not having it with fuel odor in the cabin.

Subject: Re: Gas Tank Cap Wed Aug 11, 2010 12:40 am

I have several 240 OEM gas caps. Plastic "in color" ones. Shake one, it'll rattle slightly. IMO, is vent valve rattling.