Last year my gas cap "walked away"and I went out and bought what was supposed to be a replacement - Stant 10625, large opening, vented. I struggled all year with the motor wanting to die when pulling up to stop signs, etc. Which got me thinking (dangerous!)... I pulled the gas cap off and, to my eye, it doesn't appear to be vented. Not to say that's for sure my problem, but worth making sure it's right.

​​The caps for 1949 should be vented, right? At Advance Auto I had them compare a 10625 (1950 and earlier) to a 10623 (1951 and later). If I'm looking at this right, the 10623 has a vent mechanism in the middle there, right? What's up with the supposedly vented 10625?

I've looked around at all the usual places and they claim to have the right gas cap, but never show the bottom. I might call a few of them, but I thought I'd put it out to ya'll before I make any calls. Thanks!

Gas caps: 10625 vs 10623

Edit: truck is 1949 F1 with 255 Flathead. Fuel tank is still in the cab. It was still using the mechanical pump, but I'm converting to electric... in the middle of plumbing that right now.

 

Yes, it should be vented. Go here for a recent discussion with pictures.
https://www.ford-trucks.com/forums/1...tank-vent.html

 

Thanks. I think it was actually that thread that (metaphorically) got my wheels spinning.

 

The gas cap better be vented or your truck will not run !!

 

Thanks guys. Anybody have pics of what the underside of the gas cap should look like? Or where's a good place to pick one up?

 

Why would the gas cap venting only affect the truck when it is sitting still? You may or may not have a vented cap. I cannot believe it is the root of your issue.

 

When the fuel pump sucks fuel from the tank it creates a vacuum that needs to be replaced with air, the cap has to be vented to allow air to enter.

 

I get the physics. I don't understand why the OP would have an issue only when stopped or stopping.

Remove the cap and take a drive. I'll bet the same fuel delivery problem persists.

 

Click the link in post number 2 of this thread. There is a picture of top and bottom of my cap. It clearly shows the vent hole just beside the center rivet.
https://www.ford-trucks.com/forums/1...tank-vent.html If you need a better picture, I can take a more close up shot. Someone on here has an old cap, mentioned in the thread I linked.

 

It was definately my problem however over the weekend I found that my new cap is vented with 's check valve when sucking in it allowed air but not out. The problem I found is that the gasket is so tight that when screwed in it pushed the metal behind closed and the vent from working. I have not remedied yet but is definately a problem. I'll get some pictures and an update later this evening. My symptoms where the same and I think when driving and applying fuel the pump was able to overcome the fuel starvation but at idle it was starving and would stall. I know this is my problem but I've yet to figure the perm fix to my shiny new cap

 

The #10623 has a pressure/vacuum release. This is a feature found on storage and transfer tanks to allow for expansion and contraction, and controls condensation and evaporation. It is not open freely to the atmosphere. Technically it is vented, but requires about .5" Hg to open. I would use it.

 

I just bought the Stant 10491 locking cap. It seals to the filler tube completely differently. It has a rubber "cup" that seals to the tube, and has the vent/relief valve. Very nicely made. Only $11 on Amazon. (Note: 10491 is correct for '51 -'52, I would sure like to know what's different about 48 - 50's)

 

I would, but unfortunately the 10623 is for the smaller fill tubes of 1951+.

 

Thanks, Albuq. It might be hard to tell due to the perspective, but the inner piece (with the "ears") is wider on the 1948-50 trucks.

 

The fuel filler grommet is shown to be the same for '48 - '52 on DC's site. The Parts CD shows the filler tubes to be the same for 48 - 52, although it could be that only the later type was available after '51? Caps are noticeably different -- notice the "non-spill" notation.