I guess this is a quest for information and a warning.

Have had old F100's since before they were old and encountered an issue on a 64 that I've never encountered before. Fueled up nothing unusual, pump turned off and stopped pumping did not overfill.

Drove several miles and parked at the office. After work and getting ready to head home I noticed a small wet spot under gas cap filler and saw a little drip coming from around gas cap. So I figured I'd just make sure gas cap was tight. I removed cap and gasoline exploded out of tank like a fire hose. I was soaked head to toe in gas. Woman standing in parking lot thought I had drowned in the stuff. Literally have never had that happen in over 40 years of driving these things. At least 2 gallons came gushing out really hard to say. Tank said full after fueling and 3/4 after the eruption! Filler was slightly on down hill side but nothing much. It sprayed high enough to soak my hat and face. BTW soaking your cell phone in gas isn't recommened!

Temperature was around 83 at the time.

Bad gas cap or clogged vent tube?

 

There is no vent line. The gas cap is vented. You probably have a faulty gas cap.

 

The caps on these trucks are vented...… I never fill the tank to the top unless I am on a trip and going to drive it down to at least 3/4 tank before parking, even parking on a side hill can cause the gas to run out and eat the paint below the filler. Temp at 83 will be a lot higher inside the cab and cause the gas to expand. Vented cap.

 

An unvented fuel cap . . . A full tank . . .and 8 or so hours parked in the sun . . . No further questions, your honor!

 

Repro gas cap or original?

 

Not really sure. I'd guess original but always possible Granddad replaced in the 70's.

 

Post a good pic of your gas cap and we might be able to tell if it original or not. I know, sounds weird, but it's fairly easy to at least tell if its not.

 

Not a really good pic just one I had already

 

My thought would be not original - they were painted body color originally - and not over top of chrome - this one looks like a chrome replacement cap. Very common thing to replace. If nothing else for the bling!

 

My theory is "vented" reproduction caps aren't. And that's a reproduction cap, most likely.

 

Well I rarely fill it up. And that may have been the first time I ever removed the cap after I had the solution is straight forward. Don't do that :-)
I will see if LMC or somewhere has a replacement cap (vented) that they offer.

I've had a little air come out of tank on hot days, I've just had never had the volume of gas explode out that happened this go round.

Some one needs to comment on the custom wood tool box!!!

 

If you buy another "vented" cap, it will just do the same thing. Have to get creative with a small drill bit is what I'm getting at.

 

Looks like it covers up a fender that was made for a spare tire. No other good reason I could see to extend the box back over the fender like that. Looks like a cool truck, the box not so much.

 

Copy that..

 

Just one of those funny Grand dad modifications. Old truck has hauled lots of elk out of the hills.