I now have inside parking for my supercab. When I walk towards the rear, it reeks with fumes. No leaks or drips anywhere. Then I noticed if I remove the gas cap for a bit and let the pressure out and put it back on, the fumes quit for a while. The present cap is a Stant G751. Some NOS Ford caps show up on ebay well just about every week but I don't want to get the wrong one and parts stores often don't have a clue on these old trucks.
OH, my truck does not have evaporative emission which I understand takes a different cap.
An e-bay seller told me D5TZ-9030-E which he has is the correct one.

 

Do you have the vent hose underneath hooked up correctly?

 

There's a pretty good discussion on the vent tubes here. I'll look in my subscription threads for the name and post back on here, there was some good info on the vented and non vented tanks.

 

Most ebay sellers haven't a single clue what parts fit, including this cluck.

Evaporative Emission: Unleaded fuel, non vented fuel cap. Tank has a vapor valve adjacent to the sending unit, vapor line routes along right inner frame rail to charcoal canister in engine compartment

D7UZ-9030-F (replaced D5TZ-9030-E) .. Fuel Cap - Locking-Single Cap-non vented-chrome / Use with ev/em [Evaporative Emission] (Motorcraft FC-788) / Obsolete

1975 F100/350 & Econoline from serial number W80,001 / 1976 F100/350 & Econoline.

Pic: Scroll down to 9030 - 2nd entry - Locking Single Cap. Shows D5TZ-9030-E being replaced by D7UZ-9030-F and Econoline applications, F100/350 applications are on the next page.

 

Ok thanks, obviously I have a non-vented cap on my truck. Since this isn't an evaporative emission truck, there is no rollover valve on top of the tank with the vent hose, nor is there a cannister in the engine compartment. The truck was sold new in Oklahoma which never had emission testing and still doesn't.

 

you need the vented one. the type that goes click click click when u tighten it

 

I run a parts store vented cap. It has a pressure relief valve which holds quite a bit of pressure or vacuum before it vents. Pressure means leaks or fumes and vacuum may cause vapor lock. I didn't care for that so I "fixed" it. A strategically placed 1/16" hole in the cap and no more problems.

 

vented gas caps are fitted with a one-way valve, to allow air in and not out. A 1/16" hole is defeating that, and therefore allowing fumes to leak out, and gas to evaporate...

...just saying.

 

I like everybody's input. That's what makes this site worth reading.

 

FWIW my particular cap would hold both pressure and vacuum. The "woosh" of air went both ways depending mostly on temp changes. Cool morning, "woosh" in. Move it out and park in the sun, "woosh" out.

 

Sounds like a non-vented cap intended for evaporative emissions control.

 

Could someone please confirm vented caps go click click when locking.

I have never received confirmation on how to tell a vented from non vented

 

I confirmed that in post #6. most caps these days are vented, because every car now days has SOME level of emission control on them. So it is exactly like your newer car, yes that one.

You will know the non vented, because it will lock clockwise, and not go further.

I think the vented is more common than the nonvented.

 

post your truck specs and someone can look it up at autozone or oreillys for you.

 

I have a79 f250 with a poly tank mounted between rails behind rear axle.

It turns clockwise then stops.