What specifically would cause this?

[fj40z]

I've been searching and reading al of about fuel tank pressurization due to blocked lines or the charcoal canister not venting properly, but most of the threads about fuel coming out of the filler neck are referring to pressurization with the fuel cap off. What happened to me was I was filling up and right as it got full and the nozzle kicked off gas sprayed back out. Not much at all though, got a little on the paint. Then after just a couple of seconds I could see the gas start to come out of the fill hole, then I would say close to half a gallon or more proceeds to pour out. I did not put the gas cap back on in between the time of the initial spray to when it started pouring out like crazy. It was like it over filled but went somewhere else other than the tank then came back out.

 

[Output Shaft]

Tank isn't venting properly. Check char can.
Vapor suction a gas station may not have been working properly, pressurizing the tank as you fueled.

Escaping bubble burped fuel out of the fill pipe on its way out like a baby burping too much porridge.

Fill slower near the end. Don't over fill.

 

[vipergrhd]

It's marking it's territory that's all. Try disconnecting the hose at the canister.

 

[Michael B]

Was the truck sitting at an angle allowing air to be trapped in the far side of the tank possibly?

 

[fj40z]

Maybe very slightly on angle but it was really pretty flat.

 

[FJ40Jim]

Maybe RFG coming out of the cold ground and getting bubbly in the warm Cruiser tank?

 

[TobyB]

Boiling fuel? The vapor pressure of modern 'gas' is pretty horrifyingly low.

How hot was it? Was the truck hot from a freeway run, maybe?

Or yeah, plugged vent line... maybe....

t

 

[GLTHFJ60]

My guess is that the tank is not venting properly, somehow, during the fill process. Instead of air escaping during the fill, it was being pressurized by the fuel entering and when you stopped the fill, fuel was pushed up the neck.

Was this a regular fill nozzle or one of those vapor recovery nozzles?

There is a main tank vent that vents into the filler neck when filling. If this somehow became blocked, or was otherwise prevented from venting during fill (such as a bad vapor recovery fill nozzle at the station) then it could conceivably cause this pressure.

Try the exact same process, but at another gas station. If this is a problem with the truck, it should be repeatable.

 

[DickM]

There is a fast fill breather tube that comes out of the top of the tank and runs back into the side of the main fill line where you insert the gas fill nozzle. It is the large (1/2") hose that you will see if you remove the cover shield that is in the space behind the wheel well and under the gas fill door location. There are 4 or 5 other hoses there as well because there is a manifold that the hoses attach to in order to go through the inner fender wall and get to the fuel vent stuff behind the back side panel.
I suspect that there could be a problem with this hose as I think it's job is to prevent pressurizing the tank when fuel is put in at a "fast" rate.

 

[doug720]

Ethanol in modern gas will cause old rubber parts to deteriorate. The many vents connected to the fuel tank, 1/4 panel separator. even the hoses going to the emissions canister and carb lines under the hood, all will shed rubber. This shedding can block the vents and cause this problem.

I had this happen years ago on my 60. Here in CA, we have E10, and it melted my fuel lines. When I checked the fuel lines, there was rubber "Mush" inside blocking the ports.

Plus, all the rubber fuel lines are likely 32 years old and probably due for changing. Make sure you use ethanol rated fuel lines.