When you click on links to various merchants on this site and make a purchase, this can result in this site earning a commission. Affiliate programs and affiliations include, but are not limited to, the eBay Partner Network.
I am having an issue on my truck with what seems to be a pressure situation causing some leaking in the vent tube going back to the gas cap area
I have a 1978 truck but with an aftermarket tank that does not have the vent tube for the Evap system any longer. the other day i was driivng the truck and everything was good until i got on the gas hard a few times and then when it was sitting I notced gas dropping from the connecting joing on the vent that goes back towards the cap itself. i am assuming the cap I have is no good anymore or the wrong type.
Should I be using a vented or non-vented gas cap with my setup?
Rule of thumb is that you need a vent somewhere - if the tank is vented to air or to a carbon cannister, you use a non-vented gas cap. If you have an unvented tank, you need a vented cap.
Did you do the tank swap? Do you know what cap is on it? So if you had evap, but no longer have it, you likely need to run a vented cap. A vented cap still will let air in to let the pump pull fuel out for engine use. I am not understanding where your dripping is though, isn't the vent pipe you see under the gas cap anyway. If you mean a hose leaks, maybe it's cracked. Maybe what you saw was just some slosh after ******* it with a full tank.
I think I read that the inlet where the cap attaches is somehow different vented vs non-vented? My '77 has a vented cap, no evap, and to get fuel out air has to be let in, but even a vented cap keeps fuel in.
Did you do the tank swap? Do you know what cap is on it? So if you had evap, but no longer have it, you likely need to run a vented cap. A vented cap still will let air in to let the pump pull fuel out for engine use. I am not understanding where your dripping is though, isn't the vent pipe you see under the gas cap anyway. If you mean a hose leaks, maybe it's cracked. Maybe what you saw was just some slosh after ******* it with a full tank.
I think I read that the inlet where the cap attaches is somehow different vented vs non-vented? My '77 has a vented cap, no evap, and to get fuel out air has to be let in, but even a vented cap keeps fuel in.
Yes it was leaking at the connection joint fo rthat longer thinner vent line that goes back towards the cap..the reason i am thinking my cap is part of the problem is #1--it si OLD..lol..and #2 when I remove the cap and kept driving the truck it stopped leaking
Well, IF you shut off or blocked any EVAP, you'll need a vented cap of sorts. It'll still build a little pressure, as fuel from a cold gas station ground tank warms up in a truck tank out on a roadway. Mine is vented, it will let a slow pressure rise escape, but if a sudden slosh, like roll over, will shut. It always lets air in, is a Stant # 10749 but mine being a '77 without EVAP ..... it may not fit yours.
Well, IF you shut off or blocked any EVAP, you'll need a vented cap of sorts. It'll still build a little pressure, as fuel from a cold gas station ground tank warms up in a truck tank out on a roadway. Mine is vented, it will let a slow pressure rise escape, but if a sudden slosh, like roll over, will shut. It always lets air in, is a Stant # 10749 but mine being a '77 without EVAP ..... it may not fit yours.
That is actually an issu eI had when i tried to use a vented cap...because it also allows air in the tank I came out after 2 days and had a huge puddle of gask under the tank where the pressure pushed it past the o-rin for the sending unit
Not sure itf it matters but I also have a Holley eletric fuel pump on the truck
That is actually an issu eI had when i tried to use a vented cap...because it also allows air in the tank I came out after 2 days and had a huge puddle of gask under the tank where the pressure pushed it past the o-rin for the sending unit
Might been a weak seal, uneven or bent hole, etc. It is aftermarket, and you did away with EVAP as I recall, Reads like the cap worked.
Cap looks like it got dropped AND run over a few times. It seams to have been working though. In you picture, I drew a RED circle, looks like that clamp is some loose too. Maybe needs to be moved an 1/8" towards the end of rubber and tightened where not on the bulge.
Cap looks like it got dropped AND run over a few times. It seams to have been working though. In you picture, I drew a RED circle, looks like that clamp is some loose too.
I will make sure to double check that one!
And yes that cap is VERY old, was ont he truck when I got it and never really even checked it out until i started modding the truck and having issues.
Like everyone has said, if you have a no other vents to the tank, you need the earlier vented cap. It looks to me like you have the non-vented cap, the one that only lets air in, not in AND out. I have the same style on in my Bronco. I too thought the earlier caps had the lugs that hold it in the filler tube in a slightly different position so the caps wouldn't swap as easy. Anyway, I think the real clue is the vent tube crossed over from one side to the other. I think that means your filler and tank don't match. I thought when they switched from evap to non-evap, they switched which side of the filler tube the vent tube runs on. So maybe your truck used to be evap and had a non-evap tank installed..
Like everyone has said, if you have a no other vents to the tank, you need the earlier vented cap. It looks to me like you have the non-vented cap, the one that only lets air in, not in AND out. I have the same style on in my Bronco. I too thought the earlier caps had the lugs that hold it in the filler tube in a slightly different position so the caps wouldn't swap as easy. Anyway, I think the real clue is the vent tube crossed over from one side to the other. I think that means your filler and tank don't match. I thought when they switched from evap to non-evap, they switched which side of the filler tube the vent tube runs on. So maybe your truck used to be evap and had a non-evap tank installed..
Yeah the truck most definitel was evap originally..the PO from me installed this tank since all the evap stuff was removed long before
