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Old 11-27-2012, 02:31 PM   #1
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Diesel fuel backing up the filler neck during refueling...

I'm a noobie with Diesel vehicles, and just got back from my first long trip with our Diesel SMB.

Our van is equiped with a 33gallon main (shortened to 30 gallon with U-Joint kit) and a 20 gallon or so auxiliary tank. My first fueling went fine, at a big-rig pump at a truck stop. At the fuel stops after that, fuel kept backing up the filler neck, would only go in if I trickled it in at a rate of 1/100th gallon per second or so. One pump at one station would no go that slow, and I had to abandon the fueling effort.

What gives? Do some Diesel fuels 'foam up' more than others? Do I have a clogged vent hose or two?

I can't be the only one to have ever experienced this...
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Old 11-27-2012, 06:48 PM   #2
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Re: Diesel fuel backing up the filler neck during refueling.

with my transflo I need to fill the rear tank first then the front or it has a fill issue with the vent.
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Old 11-27-2012, 08:35 PM   #3
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Diesel fuel backing up the filler neck during refueling...

I take 4 gallons after the pump stops. Total pain in the butt loaded with family while I fill at 1/100 of a gallon at a time. I need to go get the transfer flow tank Quadvan has waiting for me. ....
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Old 11-28-2012, 10:37 AM   #4
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Re: Diesel fuel backing up the filler neck during refueling.

As mentioned above, the last few gallons can take forever to fill - that is because the fuel level can cover the tank vent.

Since yours is doing it for the entire tank fillup, I would bet you have a plugged or crimped vent.

You might also check on dieselstop.com and search for 'harpoon' . It is a mod to raise the level where the tank vent is blocked.

The Ford fuel tank has a vent tube that extends down into the tank. That is supposed to leave expansion room for the fuel and prevent fuel spills. When the fuel level hits that tube, foam shoots up the vent and shuts off the pump. When I first got my 46G tank, I spent 45 minutes trying to get it full to the filler neck (stubborn!). Salem-Kroger dropped the tank, found the problem and put a hole in the vent tube that is about an inch from the top. Now it will fill quickly to within 4 gallons of the top. The expansion room is now about the same as a stock tank.

On Dieselstop.com they refer to this as 'harpooning'. You can drill a hole, hacksaw a cut, use a dremel tool, or whatever to effectively raise the vent level. The pickup guys simply cut the tube off, but theirs is plastic and ours is metal.

Mike
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Old 11-28-2012, 01:00 PM   #5
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Re: Diesel fuel backing up the filler neck during refueling.

Ah-Ha... thanks for the explanation of how the vent works, 6L Mike.

It sounds like I may have a combination of two problems... Fortunately, in the process of removing my hitch and bumper, I just cut away the factory spare tire carrier and K-shaped support structure, giving more rear fuel tank hose/hardware access now.

Who wants to come over and help me drop the rear auxiliary fuel tank?


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Originally Posted by Ford_6L_E350
As mentioned above, the last few gallons can take forever to fill - that is because the fuel level can cover the tank vent.

Since yours is doing it for the entire tank fillup, I would bet you have a plugged or crimped vent.

You might also check on dieselstop.com and search for 'harpoon' . It is a mod to raise the level where the tank vent is blocked.

The Ford fuel tank has a vent tube that extends down into the tank. That is supposed to leave expansion room for the fuel and prevent fuel spills. When the fuel level hits that tube, foam shoots up the vent and shuts off the pump. When I first got my 46G tank, I spent 45 minutes trying to get it full to the filler neck (stubborn!). Salem-Kroger dropped the tank, found the problem and put a hole in the vent tube that is about an inch from the top. Now it will fill quickly to within 4 gallons of the top. The expansion room is now about the same as a stock tank.

On Dieselstop.com they refer to this as 'harpooning'. You can drill a hole, hacksaw a cut, use a dremel tool, or whatever to effectively raise the vent level. The pickup guys simply cut the tube off, but theirs is plastic and ours is metal.

Mike
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Old 11-29-2012, 08:32 AM   #6
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Re: Diesel fuel backing up the filler neck during refueling.

I have this issue as well, but when I cut my tank open to shorten it for the Ujoint 4x4 conversion, I found that there was no long vent tube. It was already pretty short. So I think even when it's short, you still have to struggle for those last few gallons. Mine is an '03 7.3, by the way.
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Old 01-02-2013, 03:25 PM   #7
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Re: Diesel fuel backing up the filler neck during refueling.

Just returning from another 1200 mile road trip, and I am still frustrated with filling the rear tank.

Before leaving, I pulled both fore and aft tank's filler necks and vent tubes. I blew out the vent tubes with compressed air. The rear 20 gallon tank's vent tube showed no blockage at all. The forward tank was a little slow to vent pressure out of the filler neck.

On our way out of town, I filled both front and rear tanks without incident, they filled up the filler neck, with a couple extra squeezes of the handle, trickling in the last gallon or 2 as I recall.

To get a better mpg 'read', I wanted to use only the rear fuel tank, which I did.

After the first two rear tank fill ups going smoothly, I figured the shot of compressed air dislodged something, and my troubles were over.

Not so.

If the forward tank is still full, filling the rear tank is all but impossible. Even after 220miles of drawing from that tank. I tried different pumps with different driveway slants, thinking it was a filler neck level issue, but it didn't seem to matter.

Is it possible that the front and rear vents somehow tied into one another?
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