Do all gas caps vent tank pressure if it gets too high? I am asking because I dont have a charcoal canister anymore and dont have a tank pressure relief valve. Is the stock gas cap going to baloon the tank or will it release pressure at a couple of psi or something?

If the stock cap doesnt vent ever - where would I get one that would?

Thanks.

 

stock, no vents from what ive seen, id go hit up a parts store because im sure they have one in stock

 

So what do I ask for? A pressure relief cap?
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For example on this website I found, what is the difference between:

Pressure-Vacuum http://www.cgenterprises.com/fuelcaps/mgc819.htm
Vacuum only http://www.cgenterprises.com/fuelcaps/mgc825.htm
and non Vented http://www.cgenterprises.com/fuelcaps/mgc826.htm

I mean I think its that non Vented doesnt allow air or fuel vapor in our out ever, Vacuum only lets air in but no fuel vapor out and Pressure-Vacuum lets flow both ways.

I would be cool with a 2 way vented cap but I dont want it to vent at .00001 psi or something - that would be like leaving a non vented cap unscrewwed (loss of fuel due to evap costs $$$).

 

This looks promising - for 2nd gens:
http://www.parts123.com/parts123/yb....Z5Z5Z50000136d

Says its a vented cap whereas the 82-92 one says nothing about venting:
http://www.parts123.com/parts123/yb....Z5Z5Z50000136d

 

BTT

 

Most of the Gm gas caps I have from the 80's have a valve in the middle. I drilled one out to have it fully vented when I removed my canister setup, as you need to be able to let air in otherwise the tank will build too much vacuum I believe.. ie: fuel goes out, air displaces it.

I think the valve in the middle of the gascap is pressure relief though, if yours has one..

-Dave

 

mine doesnt, never have i seen a vented cap from factory on these, just goto the parts store and look at the gas cap section, match up one that fits and pick the vented one, pretty simple, or you can ghetto rig one by drilling it open

 

No drilling. What I think you want is one that vents inward at a very low tank vacuum to let air in and prevent tank vacuum but you also want the cap to hold some pressure in to prevent massive vapor loss. Well see if I can find one at the zone. If not I already tested the cap I already have and it seems to allow venting inward (vacuum relief) but I couldent generate enough pressure with my lungs to make it vent outwards. So I am not sure it will. Rockauto.com actually sells the adapter that emissions stations use to test gas caps. It has the gas cap thread into one end of it and a small hole in the other for applying pressure/vacuum. Maybe Ill just get that. Or I suppose I could take it to my emmisions station... hmm.