I just want to verify if my cap is vented or not?
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Bump, does anybody know anything on this particular cap?

 

looks vented to me,I have a ford tractor cap oval and ford blue vented that Im hoping to use on my dump flat bed,was wondering if vented caps are ok?

 

From my understanding the vented fuel caps have 4 prongs like yours, the non vented caps only have 2 prongs.

 

I was just wondering because the other day my truck was vapor locking, and I took the cap off just to make sure it was venting properly and wasn't causing a problem.
So when I losened the cap it sucked in a lot of air so I wasn't sure if it was a vented or not.

 

Not vented. If it sucked in a lot of air it wouldn't be the vented type.

EDIT: Bill says below that is a vented cap but if when you cracked it open there was a sucking sound then something is wrong. Sometimes, more often than not, a part made in certain countries are made to "look" correct but function is another story.....

Bottom line your tank needs ventilation or you will have problems.

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The pictured cap only has two protruding ears (prongs) so it's vented. Four eared non vented caps look totally different on the inside.

Non vented caps were used with evaporative emission (unleaded gas), have four ears and the ears are staggered with two ears above, two ears below 180 degrees apart.

Evap/em fuel filler tubes have restrictors in them that serve two purposes. Back then gas stations nozzles came in two diameters, larger for leaded gas, smaller for unleaded gas.

The evap/em restrictors wouldn't allow the leaded gas nozzles to fit in, would only allow 4 eared non vented caps to be used.

These trucks have a vent hose next to the fuel filler hose. The vent hose is supposed to be taped to the filler hose in three places, otherwise it will collapse.

 

So mine is a non vented cap since it has the 4 prongs?
My truck is a 79 and was supposed to have the emissions stuff but is long gone.

I did put a vent cap on the rubber hose coming off the top of the gas tank, I forgot the name of the valve that there.
So the tank has at least one vent, but it must not be enough.

 

Forgot to ask, where can I get a vented cap at?

 

Look at your cap, it has only two protruding ears, so it's vented. The vent holes are clearly visable.

Four eared non vented cap is deeper, the ears are staggered, with two ears above, two ears below, 180 degrees apart.

 

Ok I thought you were talking about the ears on the outside of the cap.

So how can I test this cap, because the other day my truck started to vapor lock, so I immediately pulled over and unscrewed the gas cap, and heard it sounded like it was sucking in air.
Or pushing air out I don't remember I'll have to double check again.

 

What in the world? That's the fuel caps handle.

If your truck originally had evap/em, it would have had a 4 eared non vented cap.

It's possible that at some point, a PO replaced the restricted evap/em fuel filler tube with one from a truck without evap emission and used the vented cap.

This was rather a common occurrence back then, because leaded gas was cheaper than unleaded gas.

 

Hello all,

I was doing a search and found this old thread to bring back to life. I have a '78 F150 Ranger. I recently changed my tank to a 38 gallon. I installed new filler hoses, straps, fuel lines, sending unit, etc. That being said, I had this problem before I changed out the tank. I have what should be a venting cap, purchased locally from Dennis Carpenter a while back. On occasion, I had issues with strong air and sometimes gas spewing out when opening the cap, even slowly. The vented cap did not help with this. Perhaps I bought a bad cap. One of my questions is, I thought the smaller filler tube was a vent line. There are two hoses, one large with the metal protective fold over cover and a smaller one. If this is a vent hose, why does it not vent? It's obviously not clogged as it is new. The emmission equipment was removed earlier and the tank removed did not have the valve hole.

Yesterday, I had probably 30-33 gallons of fuel in the tank (not completely filled). While it was parked about an hour, I noticed leaking underneath. There was over a gallon of gas on the parking lot and was nearly pouring out. When I opened the cap it spewed ALL over. There was a lot of pressure. I was at work and did not get down on the asphalt so I don't know where it was leaking from, but I assume the fuel line, as it is only clamped on with a spring clamp. does that sound accurate? Seems there would have to be a lot of evaporation to build up 5-8 gallons of empty space and push that much out. After opening cap, the leaking stopped.

Today, I removed the cap. It does have two prongs and I can see the valve. I blew in to the bottom and nothing. However, I pushed around the valve and looks like it stuck to the side. I could then blow through from the bottom. Does this mean the valve should be working now? Anyone else experience this? It is extremely frustrating to get gas sprayed all over my brand new paint job too. Plus, gas ain't cheap...
Thanks for the help. sorry to be long winded.